Meni Rosenfeld

Write a new message. Unless requested otherwise, I will reply on this page, under your post.

Welcome!

Hello Meni Rosenfeld, and welcome to Wikipedia! Thank you for your contributions. I hope you like the place and decide to stay. Here are a few good links for newcomers:

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I hope you enjoy editing here and being a Wikipedian! Please sign your name on talk pages using four tildes (~~~~); this will automatically produce your name and the date. If you have any questions, check out Wikipedia:Where to ask a question or ask me on my talk page. Again, welcome! 

Thank you for making an account.

I replied on my talk page about the square root. Oleg Alexandrov (talk) 18:42, 22 December 2005 (UTC)

oops! yes, we ARE interesting, are we not?

I am a newcomer to the Wiki-world too. Thanks for the correction! MathStatWoman 18:10, 27 December 2005 (UTC)

Your New Toolset Page is at "User:Meni Rosenfeld/Toolset"

I kind of suspected you might have wanted to prepare a general intro page (which is why I warned you). I don't know how old you are, but I get the strong feeling that the "Boomer" and following generations, for the most part, prefer "trial & error"— not something that would appeal to a mathematician— but something strongly appealing to the "Adventure Game" set. (I, myself, am a recently retired Computer Scientist— and I date from the early '50s and analog and hybrid computers.)

I am now testing the intro page. I realize the spirit of Wikipedia is more in the nature of communal activities. But I feel some obligation not to provide non-working or otherwise defective references for the newbies.

But, hey, I placed a copy on a page called User:Meni Rosenfeld/Toolset It's all yours to do with as you please! But keep track of any changes you make to the generic (true content) stuff; you may want to change the Generic Page when I make it public. (At the end of the week; I promise.)

I suggest you bookmark that page and put a reference to all your other pages in the "My Shortcuts" section.

Thanks :-)

Apparently you are doing a better work than I could have done, so I'll wait until the "official release" and then see if I have any useful suggestions. Currently what I can say is that organizing the list of articles in the form of a hierarchical list would probably be desirable.

In the meantime I will use the current version for my own quest for knowledge. :) --Meni Rosenfeld 20:34, 8 January 2006 (UTC)

Hi from MathStatWoman

Hi and thanks for the comments. I responded on the shatter page. MathStatWoman 23:33, 11 January 2006 (UTC)

hi again

I had a long holiday (8 days of candles and oily food), and did not have time for Wikipedia. I must be getting old and not getting enough sleep!!! YES, I meant unit circle! sigh...thanks...and thanks for being polite...some folks on Wikipedia are uncivil! I shall answer your other q's on the shatter page after I get some sleep -- too tired now. MathStatWoman 13:24, 12 January 2006 (UTC)

I take it that you are a jew, like myself. That's nice. Where are you from? --Meni Rosenfeld 14:31, 12 January 2006 (UTC)

Random math article

Hello Jitse, I have noticed that you have a tool for a Random article in mathematics. That is of great interest to me (please see my discussion of the issue). Do you have any remarks on what is said in that discussion? Do you know a way to make such a tool more built-into Wikipedia? --Meni Rosenfeld 16:35, 12 January 2006 (UTC)

Wow, I'm impressed that you found that. I don't have much to add to the discussion. The problem is that it is not easy to generate a list of all articles in Category:Mathematics or one of its subcategories. In my case, I basically copy the list from Oleg and I use it to generate Wikipedia:WikiProject Mathematics/Current activity (which includes the total number of maths articles, by the way); since I have the list anyway it is quite easy to pick a random article. However, the list is updated only once a day to be easy on the servers. Due to the way the database containing Wikipedia is implemented, generating a list of all articles in some category or one of its subcategories will always take a lot of time (I think, but Magnus Manske seems to think that this is quite feasible [1] [2]). I think that it will be pretty hard to generate a random article without having this list.

I'm glad to answer any other questions; I happen to know a bit about the technical side since I'm interested in getting Wikipedia support MathML. -- Jitse Niesen (talk) 21:56, 12 January 2006 (UTC)

Nah, the list is not mine, is the list of mathematics articles. :) Oleg Alexandrov (talk) 01:17, 13 January 2006 (UTC)

I'm glad I have an opportunity to make you glad :)

1. Do I understand correctly that there are (at the time of writing this message) 12151 math articles and 3208 stubs?
2. Is it possible to make your tool work within WP, without going through an external link, which seems to make the process slower?
3. Is it likely that the way categories work will change, so it becomes possible to conduct category-specific queries (num. of articles, random entry, statistics, etc.) without ad-hoc manual tools?
4. Does your tool work like the one suggested in the aforementioned discussion, making different articles appear at different probabilities, or does it employ an other method?
5. How do articles make their way in\out of the list of mathematics articles?

--Meni Rosenfeld 13:56, 13 January 2006 (UTC)

There are indeed 12151 math articles, but around 700 of them are redirects (that problem needs to be dealt with eventually). To answer your last question, articles come in either by hand, or lately, via User:mathbot (see first section). They come out via User:mathbot/Blacklist. Oleg Alexandrov (talk) 19:18, 13 January 2006 (UTC)

1. There are 12151 maths articles according to the definition at the bottom of Wikipedia:WikiProject Mathematics/Current activity. This is different from the number of articles in Category:Mathematics or one of its subcategories. For instance, Ketchup is in Category:Soft matter is in Category:Entropy is in Category:Dynamical systems is in Category:Mathematics, but Ketchup is in list of mathematics articles because Category:Entropy is blacklisted in List of mathematics categories. I think that there are a lot of articles having little to do with mathematics that are indirectly in Category:Mathematics.

2. It is theoretically possible to rewrite my tool in PHP and get it included in MediaWiki (the software that runs this website) but I think it won't be easy to convince the developers that this is a good idea. Another possibility is to put the tool on the m:Toolserver so that it can talk to the database server directly.

3. My guess is: not in the short term (say within one year), but quite possible within say five years.

4. No. It picks a number n between 1 and 12151 and then it returns the nth article, so every article should have the same probability (assuming that the random number generator in PHP is truely random).

Oleg, I thought that your bot didn't list redirects? Admittedly, my knowledge comes from an unreliable source :) -- Jitse Niesen (talk) 22:10, 13 January 2006 (UTC)

Answer to your question 1

Hi, See discussion on shattering for my answer to one of your q's. More when I have time.

Cheers.MathStatWoman 21:05, 13 January 2006 (UTC)

Wikipedia:Starter toolset

A page by the above name has been created to assist newbies. It is an eclectic index into Wikipedia. Here's hoping it will arouse some interest in improving upon it. —>normxxx_talk—> email 07:35, 14 January 2006 (UTC)

Thanks :-) --Meni Rosenfeld 13:35, 15 January 2006 (UTC)

hi

The weekend has ended, Shabbat and the day after to recover from Shabbat, and time again for work, school, and Wikiworld. So here we are.

Back to your q's:

1. About subsets, we probabilists do indeed use the notation that I used, but if it bothers set theorists, and I change it, then the notation will annoy the probabilists. Sigh... we cannot satisfy everyone... I really want to leave it as it is, but if Wikipedia demands otherwise, let me know, and we'll discuss it further.

2. We settled that, right?

3. More to come on empirical process article as I get time between work, research, school. Thanks to everyone who entitled that article well and re-directed it properly.

4. About discussing distribution functions (df's): [incidentally, probabilists, when doing serious research, do not use the teminology "cumulative" df's(cdf's), but just df (see all the peer-reviewed papers in Ann.Prob,. J.Appl Prob, and texts such as Loeve's on the grad level); cdf is used for undergrads, though.] Anyway, in the article on shattering, we re-cast df's in terms of collections of sets because this is a very important example: we want to study sets on the real line of the form { v : v ≤ x }, that is, sets of values that are less than or equal to x. Let C be the collection of all such sets on the real line, that is, of the form , { v : v ≤ x } for all real numbers x. This is not done in the article on df's because it does not belong there; it belongs in the article on shattering. It really is vital to discuss it in the article shattering. It is an example that appears in many peer-reviewed articles on shattering.

Cheers, MathStatWoman 13:25, 16 January 2006 (UTC)

Hi.

It is in general better to discuss matters relevant to a specific article in that particular article's talk page, especially when the original discussion took place there. You don't have to worry about me noticing it since it is in my watchlist (as are all other pages I've edited). If in doubt, you can always refer me to it in my talk page. I will reply now at Talk:Shattering. --Meni Rosenfeld 19:29, 16 January 2006 (UTC)

BTW, I've noticed that you don't use edit summaries (the remark that appears near your edit in the page history) very often. It is considered bad practice to edit an article without an edit summary, because this way people have a hard time telling what you did and why you did it. Using edit summaries in talk pages is also desirable but not as critical as in articles. Besides, there is a nasty robot that can calculate the edit summary usage of the innocent and squeal to its evil master, the big man. And you don't want to upset him :-) Seriously though, if you ever try to become an administrator, mathbot will calculate your edit summary usage, and having too low a rating will make Oleg (and possibly others, though he is the most obssesed about it) vote against you. --Meni Rosenfeld 20:07, 16 January 2006 (UTC)

Thanks for the advice

Thanks for the useful advice. All that info is good to know. How did you learn so much, so fast? MathStatWoman 21:41, 16 January 2006 (UTC)

I probably have more time to spend in WP. --Meni Rosenfeld 07:49, 17 January 2006 (UTC)

Just letting you know

Wikipedia:Requests for CheckUser :- CheckUser confirms that user:DeveloperFrom1983 (talk • contribs) is a sockpuppet of user:MathStatWoman (talk • contribs). Kelly Martin (talk) 17:11, 15 January 2006 (UTC)

thank you for help

thank you for help about 'decipher a ciphertext by a simple Caesar sipher.'

No problem. Just remember to post factual questions (as opposed to questions about using wikipedia) at the reference desk.-- Meni Rosenfeld (talk) 16:02, 22 January 2006 (UTC)

about a substitution cipher

dear Meni: I am not clear about your answer, I just want to know how to decrypt the message zycu. "given f(x)=23x 10 (mod 26) is a bijection(one to one and onto) that it can be used as a subtitution cipher, then decrypt the message ZYCU was enctypted by using the function."

                                                 thank you

Help Desk

Those will be very useful! Thanks for the information. I especially like that they can be specialized for each section of the Reference Desk. Thanks again. -- Natalya 20:34, 25 January 2006 (UTC)

I love it! That makes it so much easier to direct them to a specific article. Thanks for letting me know. -- Natalya 18:05, 9 March 2006 (UTC)

Refdesk template issue

Thanks for your comments! I agree completely and appreciate the constructive tone. Cheers, rodii.

Jeanna Giese

Thanks. How come you are only active in the english wikipedia? Omer Enbar 17:13, 21 February 2006 (UTC)

Well, first, seeing all sorts of WP technical terms translated to hebrew, such as "User talk namespace" appearing as "מרחב שם שיחת משתמש", gives me the creeps. Second, with no offense, I get the impression that the hebrew WP tends to attract those that are not very fluent in English writing for those that are even less fluent, and such people tend to be less knowledgeable - affecting the quality of their work. Third, one of the forces driving WP is sheer quantity of contributors - The more users are active in a project, the greater the probability that a given topic will be covered accurately - And this is true not only for articles, but also of the project process. Since the number of people active in the Hebrew WP is negligible compared to the English one, I am not likely to find useful information there, or to believe that contributing there is worth the effort.

I hope you do not find these explanations too snobbish. Ultimately, it all comes down to cost-effectiveness: Since I have no problem understanding English, it is just more worthwhile for me to be active in the English WP. -- Meni Rosenfeld (talk) 17:34, 21 February 2006 (UTC)

Of course not, every person is free to do as he is pleased. There are many wikipedians among the heWP that are fluent English speakers such as myself (many are mathematicians). About your third point, it is true, there are not enough people currently writing in the Hebrew wikipedia, and that is why it is in need of more writers. The only "positive" side is that current contributors influence WP much more. I have read your contributions here, and I hope I'll see you in the heWP sometime in the future.

Best regards. Omer Enbar 18:41, 21 February 2006 (UTC)

Perhaps, perhaps not. Tomorrow never knows. Could take several years though. And even if I do, I don't know if we'll meet - I'm more the Durak type than Yaniv :-). Best wishes. -- Meni Rosenfeld (talk) 18:54, 21 February 2006 (UTC)

Indeed. Though more commonly I play skat. Omer Enbar 18:58, 21 February 2006 (UTC)

Thanks!

Thanks for your help in answerimg my question about "including my article in a broader search." (Phoebe R. Berman Bioethics Institute) When you get a chance, could you let me know how to add redirects to my article? Also, is there any way to make my article come up as an option when someone searches for something more vague, such as "bioethics"? Thanks so much! Kathychen 19:42, 24 February 2006 (UTC)

Okay, your article probably doesn't appear in search just because it's new. When the database gets updated, it should also appear in vague searches. But the point is that the default for the search box is "Go" and not "search" - So if you enter "Bioethics" and just click enter (which is what most people will do), you will go directly to the Bioethics article and not to a search. Only when an article with this name does not exist, pressing enter will do a search.

Now, to create a redirect, first create an article for the alternative name - For our example we'll use "Berman Bioethics Institute". One way to do it is enter this name in the search box and clicking "Go" (and not pressing enter, which will do a search). Then click on the red link "create this article". Now add to the new article this text:

#Redirect [[Phoebe R. Berman Bioethics Institute]]

Write an edit summary like "Creating a redirect to Phoebe R. Berman Bioethics Institute", click "save page", and you're done. Repeat for every name you wish to redirect, but avoid redirecting from names for which it can be argued that they shouldn't redirect to your article. -- Meni Rosenfeld (talk) 09:09, 26 February 2006 (UTC)

Thank you! Kathychen 15:20, 28 February 2006 (UTC)

Trajectory of a projectile with air drag

Was that helpful? I could have sworn I had a differential equations textbook which explained how to calculate asymptotic expansions for solutions, but I can't find it. Arthur Rubin | (talk) 17:38, 25 February 2006 (UTC)

Yes, thanks! It will probably take me a while to work out all the details, but I guess I'm on the right track. -- Meni Rosenfeld (talk) 08:54, 26 February 2006 (UTC)

New articles

Hello. I noticed at the help desk that you seem to think that a newly created article needs "a few weeks" before it can be searched for. This is not the case, a newly created page will be able to be searched for immediately or if thing are running slowly then in a few minutes. Please contact me on my talk page if you need any further help or discussion about this. hydnjo talk 16:14, 9 March 2006 (UTC)

I know for a fact that new articles don't appear in a search. Of course if you type precisely the name of an article or a redirect, you will get to the article. But if you make a search, you will find all articles containing a phrase, but only those that have been around long enough. If you don't believe me, try my examples: searching for "Lenohard" will give you all articles including the phrase "Leonhard", but searching for "Fedigan" will not yet lead you to anything. This is a known fact. -- Meni Rosenfeld (talk) 16:19, 9 March 2006 (UTC)

...Does that mean you agree? -- Meni Rosenfeld (talk) 16:28, 9 March 2006 (UTC)

I don't really know how long it takes as I hardly ever use WP's Search function. WP search has so many weaknesses such as case sensitivity and spelling rigidity that I quit using it. Instead I use Google's WP specific search engine which is much more tolerant of my mistakes. hydnjo talk 16:40, 9 March 2006 (UTC)

Oh, and I also have no idea how long it takes for Google's crawler to update. hydnjo talk 16:43, 9 March 2006 (UTC)

It seems that we have been victims of chronology. Am I correct in now realizing you've posted in my talk page before reading my clarification at the help desk? In that case, thanks for your desire to help. At first I thought you posted it afterwards, so it irritated me quite a bit.

Regarding your new post: I use Wikipedia's search every now and then, but have learnt that its database isn't updated frequently mostly by answering to people asking why the article they have created doesn't appear in the search. (btw if you want to reply, you can do so here). -- Meni Rosenfeld (talk) 16:45, 9 March 2006 (UTC)

Yeah, we're just too fast for our own good! Sorry about the mixup as my brain's frame of reference is the Go rather than the Search button. hydnjo talk 16:58, 9 March 2006 (UTC)

Yeah, the point is that I guess most users, myself included, just press "enter", which acts like "go" when there is an article with the exact name, and like "search" otherwise. This, and the delayed update thing, confuses many people. -- Meni Rosenfeld (talk) 17:02, 9 March 2006 (UTC)

I also meant "enter" for "Go". Now that you've piqued my interest, I'm goin to keep watch for the Linda Marie Fedigan article to show with Google's and WP's search engines just to see how long it does take for the annotated versions to appear. hydnjo talk 17:40, 9 March 2006 (UTC)

Good idea. Don't hold your breath, though; I've seen articles a month old not appearing in search. -- Meni Rosenfeld (talk) 17:54, 9 March 2006 (UTC)

Help desk header

This method doesn't seem to be averting all the Ref Desk questions. I have a sneaking suspicion that it may be caused by 1 of 2 things:

1. If the instructions are too long and complex, people just skip them.
2. People don't like to be told what they can't do.

Therefore, I was trying to minimize the instructions and keep them positive. I'll give it another shot. --Go for it! 19:56, 9 March 2006 (UTC)

Gosh, understanding humans is hard :) I guess your hypotheses are true, but still, if you don't tell people what they shouldn't do, you don't get any chance to convince them not to do it. As long as the instructions are clear, concise and polite, I don't think people will have trouble following them. -- Meni Rosenfeld (talk) 20:01, 9 March 2006 (UTC)

template help

thanks for the template advice (on the helpdesk page). I've begun reading the talk pages and will soon do some testing. They are a bit esoteric, but fortunately invoking them seems reasonably easy. Thanks! MattHucke^(t) 16:09, 10 March 2006 (UTC)

Wiki-star:Help

• Wiki-star: Hello there. Yes we have met before, and its why i've come here. I need your advice or help on how to insert image screenshots. I have all the questions posted On March 11 in the Help Desk. You can go there if you really want to know why i need help with the screenshot! So what do you say?

Thanks! Wiki-star 07:12, 11 March 2006 (UTC)

I've replied to your question at the help desk. Note the usage of indenting: If you start a thread, it's best to do it without indenting, and continue to use no indenting throughout.

If you reply to a post, remember to indent whenever you start a new line (click "Edit" on this section to see how I indented).

Also, when linking to a page inside wikipedia, it is better to make an internal link using double brackets: [[Wikipedia:Help desk]] will become Wikipedia:Help desk. See also my link above for some additional tricks, and don't forget to read How to edit a page. -- Meni Rosenfeld (talk) 08:09, 11 March 2006 (UTC)

Trapezoid

Just a note to say thank you for your assistance on the formula, I have verified it- privately, of course- and discovered the errors you have mentioned, correcting wherever I could. I AM sorry that the wrong information has stayed on Wikipedia for so long, and grateful that you came to assist me. The question is that my education in mathematics is somewhat strangely developed- my interest for it has developed to fanaticism, and in many respects I have educated myself or tried to prove things out, just to satisfy my interest and curiosity. We have not yet done trignometry at school, and my knowledge of it was mainly self- taught, and thus sometimes defective. I am afraid I do not know the identity you have mentioned, but shall doubtless find out more about it myself. My ability is also very strangely developed- I am afraid I have not done dimensional analysis at all, but I have taught myself relativistic mathematics, and differential calculus. Luthinya 17:48, 15 March 2006 (UTC)

How do you do, sir. It's yet another note from me and once again it is to thank you on the marvellous help you have provided for me, relating to the formula. Seeing these advice also reminded me of another thing I adored about mathematics- it allows you to express very complex ideas so succintly, yet never once looses the initial beauty of the idea.

As far as mathematics itself is concerned, I tend to view it in a similar model to Pygmalion's ivory virgin, an art at once so cold and precise, like the beauty of sculpture, yet endowed with a grace so celestial and unearthly, as of a most wondrous maiden, waiting only to be roused by the breath of a spring wind. To see her figure is to be ecstatically tantalized, yet one is also filled with a curious regret, upon touching her sides, to know that she is unfortunately not of the flesh. In any case, the beauty of nature is explicit through geometry, especially fractal geometry. Yet one must not confuse between the symbol of nature and nature itself, the latter being more wondrous than we will ever make of it.

I hope these opinions have somehow been amusing for you to read and not wasted your userspace. Delete them if you like. Luthinya 12:37, 16 March 2006 (UTC)

Of course, my talk page has plenty of space, and I wouldn't delete anything posted in it. However, I can't really say I'm art-inclined enough to fully appreciate your description - But what's important is your admiration for mathematics, which I, of course, share. -- Meni Rosenfeld (talk) 08:45, 17 March 2006 (UTC)

pi as 3

em actually i have been told on sevral occasions by engineers (my my maths teacher's brother and engineers who visited the school) by the way did you thing i just made that up? never mind

Barnstar

Thanks! I've put it in my userpage. Don't forget, though, that others are\were also involved in this thing, like Schwarzm, Ilmari Karonen, Jnothman, Go for it! et al. -- Meni Rosenfeld (talk) 19:03, 25 March 2006 (UTC)

You deserve it! It would not be good to forget the other contributers - thanks! -- Natalya 19:25, 25 March 2006 (UTC)

need help

I have a question. If I find an article and nkow that it needs to be improved, What tag shoud I stick on that article? Is there such a tag? What will this tag to to the article? Will it make it more visible to other editors(will it put it into a special list of articles that need to be improved)?--BorisFromStockdale 21:11, 25 March 2006 (UTC)

See Wikipedia:Template messages/Cleanup for some tags you can use. Among other thıngs, thıs wıll put the artıcle ın a category, where people lookıng for somethıng to do can notıce ıt. -- Meni Rosenfeld (talk) 15:03, 26 March 2006 (UTC)

Template:RD2

What was wrong with the original template? The old one worked. In this new one, the "click here"-link doesn't work properly. - Mgm|^(talk) 11:37, 3 April 2006 (UTC)

• Here, I'll show you:
  • Have you tried Wikipedia's Reference Desk? They specialize in knowledge questions, and will try to answer any question in the universe (except how to use Wikipedia, since that's what this Help Desk is for). For your convenience, here's the link: Reference Desk (when you get there, just select the relevant section, and ask away). I hope this helps.
  • Have you tried the Science section of Wikipedia's Reference Desk? They specialize in answering knowledge questions there. For your convenience, here's the link to post a question there: click here. I hope this helps.
  • You might find what you are looking for in the article about Sun. If you cannot find the answer there, click here to post your question at that article's talk page. If that doesn't solve your problem, you can try asking your question at Wikipedia's Reference Desk. They'll be glad to answer questions about anything in the universe (except about how to use Wikipedia, which is what this help desk is for). I hope this helps.

-- Mgm|^(talk) 11:40, 3 April 2006 (UTC)

• I guess that's solved. Wonder what was wrong. Would still like to know what made you decide to split it up, though. - Mgm|^(talk) 11:40, 3 April 2006 (UTC)

The current {{RD2}} and {{RD3}} only work when substed. This is actually a plus, since it will make sure everyone will subst them. The problem with the old template is that when substed it put this in the code:

{{qif|test=|then=You might find what you are looking for in the article about [[]]. If you cannot find the answer there, [{{fullurl:Talk:|action=edit&section=new}} click here] to post your question at [[Talk:|that article's talk page]]. If that doesn't solve your problem, you can try asking your question at Wikipedia's [[Wikipedia:Reference desk|Reference Desk]]. They'll be glad to answer questions about anything in the universe (except about how to use Wikipedia, which is what this help desk is for). I hope this helps.|else={{qif|test=|then=Have you tried the [[Wikipedia:Reference desk/| section]] of Wikipedia's [[Wikipedia:Reference desk|Reference Desk]]? They specialize in answering knowledge questions there. For your convenience, here's the link to post a question there: [{{fullurl:Wikipedia:Reference desk/|action=edit&section=new&editintro=Wikipedia:Reference_desk/How_to_ask}} click here]. I hope this helps.|else=Have you tried Wikipedia's [[Wikipedia:Reference desk|Reference Desk]]? They specialize in knowledge questions, and will try to answer any question in the universe (except how to use Wikipedia, since that's what this Help Desk is for). For your convenience, here's the link: [[Wikipedia:Reference desk|Reference Desk]] (when you get there, just select the relevant topic, and ask away. I hope this helps.}}}}

This is both a lot of cumbersome junk, and also transcludes the qif template - so the whole point of substing the template is defeated. The new templates are much cleaner. -- Meni Rosenfeld (talk) 15:47, 3 April 2006 (UTC)

I appear to have been blocked.

I appear to have been blocked but don't understand why. Yesterday I asked a perfectly innocent question and received a very terse answer from Erik to which I edited a thankyou note with a supplementary question, and then having saved it I noticed I had misspelt Erik as Eric so I tried to correct it but was told I had been blocked. Surely that cannot be fair? Please advise and unblock me if you agree. Thanks. [email protected] 09:58, 17 April 2006 (UTC)

Regret to advise I most definitely appear to have been blocked.

Thanks for your response advising I had not been blocked - but - I just tried to re-edit the mistake I discussed earlier and got the message that either my name or my I.P. had been blocked and when I checked the blocked list, my I.P. was there for the 16th April.White Squirrel 14:17, 17 April 2006 (UTC)

Thanks for your concern

Thank you, Meni, for your appearance on User talk:Sean Black regarding his capricious block of my account. He's popped up briefly, but without diffs to support his claim that I'd violated WP:3RR, which I am quite certain do not exist - I assume he's realized that by now. We'll see what happens.Timothy Usher 06:18, 4 May 2006 (UTC)

No problem. I will have to remark, though, that my concern was less with your case (the specifics of which I am not familiar with), and more with Sean's recent apparent tendency to disregard comments left in his Talk page. -- Meni Rosenfeld (talk) 10:54, 4 May 2006 (UTC)

Thank you

Thank you very much for your help. --Alf 16:54, 8 May 2006 (UTC)

No problem. -- Meni Rosenfeld (talk) 17:02, 8 May 2006 (UTC)

math on Hebrew Wikipedia

Hello Meni. I was reading our article on the Hebrew Wikipedia, which says that "The Hebrew Wikipedia is renowned for its high standards of mathematical articles". I have to say, this comment makes me a bit jealous, as I consider our math coverage at en.wikipedia to be quite good (compared to other online sources). I noticed on your userpage that you are a Hebrew speaker, and of course I've known you for a while around here as a mathematically minded editor. I was just wondering, are you also familiar with the Hebrew wikipedia? Are you familiar with its math coverage? Would you be able to make some anecdotal comments about how good their math coverage is (especially as it compares to ours)? I just wonder how seriously I should take their claim of expert math coverage. -lethe ^talk 10:29, 11 May 2006 (UTC)

Unfortunately, I am not really familiar with the Hebrew Wikipedia. But from what I've seen, it doesn't cover nearly as many topics as enWP (my guess is, around 500 mathematical articles), and these tend to be shorter. The content that does exist seem to be of decent quality, but IMO not as good as what we have here. So the math coverage on heWP is certainly worse than on enWP. That doesn't necessarily mean the statement you quote is incorrect, if you take all the relative factors into consideration (enWP in general vs. heWP in general, math in heWP vs. other subjects in heWP, math in heWP vs. other math sources in Hebrew). In any case, if there's anything specific you want me to compare, I'd be more than happy to. -- Meni Rosenfeld (talk) 12:52, 11 May 2006 (UTC)

Math is better covered in other wikipedias? Now that's surprising. Mathbot 15:49, 11 May 2006 (UTC)

Hmm.. I had a suspicion that it might be the case that that statement was only meant to be relative. No, I don't want any specific comparison, just some informal observations from a Hebrew speaker, which you've given me. Thank you. -lethe ^talk 17:24, 11 May 2006 (UTC)

Happy Birthday!!

Steveo2 11:01, 16 May 2006 (UTC)

Thanks! -- Meni Rosenfeld (talk) 11:33, 16 May 2006 (UTC)

Hello friend. I wish you a very happy birthday, one day late - yesterday I was away and so I missed the party. I learnt of the same from Wikipedia:Esperanza. All the best for the coming year. --Bhadani 16:31, 17 May 2006 (UTC)

Thanks to you as well! -- Meni Rosenfeld (talk) 17:43, 17 May 2006 (UTC)

Marco Polo discussion

Thanks Meni for your reply.

I will keep my nose out of Marco Polo discussion from now on. I hope they just delete the vandal posts and stop putting my ip number up. If they do i will keep deleting them. This Eugameo and his many alias names keeps calling me a vadal just because i posted some facts and evidence that Marco Polo is not Italian. A document written by an Italian in those days clearly says Marco Polo is Dalmatian and originated from Dalmatia. Countless other sources written by Italians and other non Croatians support this view. If he was born on Korcula and most agree the chances of him being Croatian are very high. Korcula was mostly populated by Croatians in those times. Many documents of those times also show that Polo and De Polo last name was Italianised under Venice rule of Dalmatia, so all these Polos and De POlos from Venice and Korcula were in fact Croats. Last but not least Iam Montenegrin so I think i would be unbias in my view of the matter.

I have nothing agianst the Italian people just Euganeo who so contradicting. He said Croat names were Italianised but Marco Polo did not...how silly when proof suggests he did.

Peace

Evergreen Montenegro

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Average and Over (runs) and (hands lost)

Thanks for renaming and straghtening out these two articles. I knew nothing at all about these terms before I started copy-editing them (which they badly needed).

Now that I see the two articles in their context, have looked at the few articles that link to them, I know something about them and I believe they should be merged. There could be one short article on Average and Over, with explanations of the two varieties. I can write the copy, but I don't know how to merge the articles, or propose the merger, or whatever is done. They are pretty obscure articles, so if there's a quick way to merge them, IMHO that is what should be done.

Either do what you know how to do, or leave word on my Talk page, or both. Thank you. Lou Sander 16:33, 20 July 2006 (UTC)

Wikipedia:Merging and moving pages has some guidelines regarding mergers. I think these articles aren't important enough to make a big deal out of the merger (proposing the merger, discussing it, building consensus, etc.), but rather it can be done immediately. The best course of action would be: Write the new article at Average and over (note that "over" shouldn't be capitalized); then blanking the two sub-articles and replacing them with a redirect to Average and over, with an edit summary explaining that the articles have been merged. The page Average and Over, since it already exists, can also be made into a redirect to Average and over. -- Meni Rosenfeld (talk) 19:39, 20 July 2006 (UTC)

Done! I tried to take care of all the permutations and combinations of capitalization, terms in parentheses, etc., but dealing with all these near-identical articles may have fouled me up. One thing I didn't do -- the former articles, now redirects, had brief discussions; I didn't delete them, because I wasn't sure it's proper to do so. Lou Sander 21:42, 20 July 2006 (UTC) PS - My family is on Israel's side in wars and other conflicts. Be safe.

Also, the article still doesn't quite ring true (the originals were very badly written). I've ordered the reference book from my public library, just to check it out. Lou Sander 21:44, 20 July 2006 (UTC)

Ok, great! As for the talk pages, what I would normally do is move them to the talk page of the new article; however, becuase the page already exists, doing this seamlessly will require administrator intervention - which is not such big a deal, but still, this is hardly worth the trouble. No harm will be done by leaving those pages where they are. Checking the validity of the article in the reference will also be great. -- Meni Rosenfeld (talk) 13:41, 21 July 2006 (UTC)

Thanks again for your help in all this. The final chapter will be written when the library book comes in. Lou Sander 15:03, 21 July 2006 (UTC)

HELP!!! The article Average and over (hands lost) seems to have come back alive. It may have something to do with conflicting or simultaneous edits by you and by me. As far as I'm concerned, all articles on the baseball term "average and over," including versions with the modifiers "(runs)" or "(hands lost)," regardless of capitalization, can and should now be properly redirected to Average and over, which, though brief, covers it all. Am I wrong, did I kill it improperly or fail to kill it, is there a better way to do this, etc.???? Lou Sander 15:00, 22 July 2006 (UTC)

There were some problems with Wikipedia's database around the time we were editing these articles. I don't know any details, but this probably has something to do with it. I've reinstated the redirect - hopefully this time it will stay. I have also put a link to Talk:Average and over (hands lost) in Talk:Average and over, in case anyone is interested in those comments - not really the right way to do things, but probably the best we can do without unnecessary effort. -- Meni Rosenfeld (talk) 06:34, 23 July 2006 (UTC)

Thanks again! Lou Sander 13:06, 23 July 2006 (UTC)

The reference book came in, and I've corrected the Average and over article. Earlier versions were puzzling because they didn't mention the vitally important fact that this statistic was presented as the result of an integer division (the average) plus the remainder (the over). I knew there was something fishy about it! Lou Sander 17:07, 15 August 2006 (UTC)

Great, I'm glad you were able to sort this out. -- Meni Rosenfeld (talk) 17:59, 15 August 2006 (UTC)

Integrals and floor functions

Here is the question. It is for a math competition.

Given that $f(n)=\int _{0}^{floor(n)}\lfloor x\rfloor dx$

(For some reason it wouldn't let me write $\lfloor n\rfloor$ as the upper bound of the integral, so I improvised)

Evaluate $\int _{4}^{5.5}f(n)dn$

--Codeblue87 20:19, 29 July 2006 (UTC)

Looks ok, but if it's a competition, I'd be extra careful. We don't want to discriminate against examinees which may have learned stricter definitions - this issue might confuse them. Will it be multiple choice or open? In either case, a good idea would be to give an example for f after the definition, so it's something like this:

Given that $f(n)=\int _{0}^{\lfloor n\rfloor }\lfloor x\rfloor dx$
(for example, $f(3.2)=\int _{0}^{3}\lfloor x\rfloor dx=3$)
Evaluate $\int _{4}^{5.5}f(n)dn$.

-- Meni Rosenfeld (talk) 20:52, 29 July 2006 (UTC)

Alright, I'll include an example. Just out of curiosity, what did you get as the answer? --Codeblue87 21:07, 29 July 2006 (UTC)

Off the top of my head, it's f(4) 0.5f(5) = 6 0.5*10 = 11. -- Meni Rosenfeld (talk) 21:11, 29 July 2006 (UTC)

Great. Thanks again for all your input! --Codeblue87 21:29, 29 July 2006 (UTC)

No problem. -- Meni Rosenfeld (talk) 21:31, 29 July 2006 (UTC)

Help Please

Hello. I was looking for someone who is He-n to help with a very quick translation related to a disambiguation project that I am on. If you have a moment, could you please take a look at Talk:Rimmon and either comment there or edit the artcicle accordingly? Thanks in advance. --Brian G 23:59, 31 July 2006 (UTC)

I've replied in Talk:Rimmon. -- Meni Rosenfeld (talk) 04:45, 1 August 2006 (UTC)

Thank you very much. --Brian G 09:40, 1 August 2006 (UTC)

Proper Formatting

Thank you for your assistance. The process is quite daunting. I am trying to put a biography on my company into the database because we have recently been the focus of a lot of media attention due to our projects in the Hurricane Katrina area. We are not trying to advertise, but trying to get factual information out because some of the articles printed recently have contained a lot of rumors.

My posting has been tagged as advertising even though I tried to make it very neutral. Is there a place or person whom I might consult for specific recommendations on my posting to prevent it from being thrown off the site? Thank you. —Preceding unsigned comment added by Angikay2 (talk • contribs)

Writing an article about oneself or one's company is always a problem, and is frowned upon in Wikipedia. Even if you do try to make it neutral, you can never be truly objective (see WP:AUTO). Also, Wikipedia has certain notability standards (see also WP:CORP), and the assumption is that if no one has written an article about your company so far, it is probably not notable enough to be included on Wikipedia. Also, the reason you describe for writing the article isn't entirely valid. My suggestion is, first of all, to check out Talk:Paradise Properties Group - Mattisse has mentioned there several things you should be aware of. You can explain there why you think this article belongs on Wikipedia or any other questionable issues. Also, don't forget signing with the ~~~~ thing. -- Meni Rosenfeld (talk) 19:06, 11 August 2006 (UTC)

Thanks

Thanks for your helpful answer to my question on the help page! Ccrrccrr 13:27, 12 August 2006 (UTC)

No problem. -- Meni Rosenfeld (talk) 13:52, 12 August 2006 (UTC)

thanks

thank you but if you could elaborate more i will be grateful —The preceding unsigned comment was added by Shaily iitian (talk • contribs) .

Continued at Wikipedia:Reference desk/Mathematics. -- Meni Rosenfeld (talk) 09:59, 17 August 2006 (UTC)

For you

Thank you! I've put it in my userpage. Of course, you are doing a lot of hard work at the help desk yourself :-) -- Meni Rosenfeld (talk) 05:00, 13 September 2006 (UTC)

Suggestion to Mac Davis

You think I should do it? I found the time stamp to fill up more space than helpful to me. — [Mac Davis] (talk) (Desk|Help me improve)

Thanks

Thank you for answering my question at the Helpdesk. --After Midnight ⁰⁰⁰¹ 22:12, 13 September 2006 (UTC)

No problem. -- Meni Rosenfeld (talk) 07:48, 14 September 2006 (UTC)

In-place WYSIWYG math and table editor

My kingdom for an in-place, WYSIWYG, wikitext math and table editor. Heck, an OpenOffice plug-in to use a wiki as a back-end would be pretty darned handy! Know of anything in this approximate constellation of tools? -- Fuzzyeric 04:53, 15 September 2006 (UTC)

Unfortunately, no. But then again, I don't know much. You may be able to find something in Wikipedia:Tools and especially Wikipedia:Tools/Editing tools. If not, there are some highly informed people hanging around at Wikipedia talk:WikiProject Mathematics, where you can ask. -- Meni Rosenfeld (talk) 15:33, 15 September 2006 (UTC)

Thanks for your answer.

Thanks! Auroranorth 11:16, 17 September 2006 (UTC)

No problem. -- Meni Rosenfeld (talk) 13:18, 17 September 2006 (UTC)

Edit Summary in retrospect

Thank you Mark! Wwhere exactly and how exactly would I change the wikicode on the page? Would I add something like "Pricing details for NZ added" where I made the change, and then put this also in the edit summary? Regards, Drahmad 05:33, 18 September 2006 (UTC)

It's Meni. I've replied at the help desk. -- Meni Rosenfeld (talk) 05:38, 18 September 2006 (UTC)

GRRR! Sorry I got the name wrong Meni!! Thanks again and feel free to delete this section as you see fit :) Drahmad 05:42, 18 September 2006 (UTC)

No problem. Don't worry, my talk page has plenty of space. -- Meni Rosenfeld (talk) 05:53, 18 September 2006 (UTC)

Now that you saw my (multiple) edits to the Wii page, is it considered poor form/bad etiquette to perform "multiple" edits to reach the end goal? The main reason I had those "micro-edits" was that I was afraid I might destroy the whole page by making some formatting mistake, so did things one at a time to ensure that I didn't stuff it up. It helps now knowing that I can "revert" a page, and I will also copy and paste the code somewhere until I'm satisified I can put it back together again if needed. Drahmad 07:09, 18 September 2006 (UTC)

Strive for balance. Don't make dozens of micro-edits, but don't make a single huge edit either. Other than that, do whatever's comfortable for you - You'll get a sense of what's optimal as you gain experience. And don't forget, the "show preview" button is your friend when trying to avoid messing things up. -- Meni Rosenfeld (talk) 08:26, 18 September 2006 (UTC)

Thank You

Thank you for your reply, I compleatly forgot that Wikipedia is pretty much global, and on another note that was a fas reply! Have a nice day---Seadog.M.S 16:25, 18 September 2006 (UTC)

No problem. Thanks! -- Meni Rosenfeld (talk) 16:28, 18 September 2006 (UTC)

division by zero

Why does the comment you removed not belong there? The range of the tangent and cotangent functions should be viewed as the real projective line with only one point at infinity. Michael Hardy 17:45, 19 September 2006 (UTC)

Hi, I've continued this at Talk:Division by zero#Trigonometry in the real projective line. -- Meni Rosenfeld (talk) 18:01, 19 September 2006 (UTC)

Finding coefficients of a series

If you don't mind my asking, what's your f(), or at least what values do you have already? It might be possible to coerce your definition of f() into a form amenable to inverse z-transformation. -- Fuzzyeric 18:07, 19 September 2006 (UTC)

Asking never hurts, of course. I am both interested in a general method for dealing with such cases, and also my eyes are currently set on the harmonic numbers, with:

$f(n)=\sum _{k=1}^{n}{\frac {1}{k}}-\ln {n}-\gamma$

Though there certainly are analytic ways to deal with it, I am currently interested in the possibility of exploring it numerically. -- Meni Rosenfeld (talk) 19:51, 19 September 2006 (UTC)

Then you might be interested in Brent-McMillan and references for fast evaluation of rational series and the Euler-Mascheroni constant. The harmonic numbers can also be evaluated using the digamma function since ^ref

$f(n)=\gamma \psi _{0}(n 1)\$

and the digamma function has several analytic expressions. ^ref -- Fuzzyeric 22:09, 19 September 2006 (UTC)

Also, you might do the following for your fitting...

• Instead of starting the harmonic (partial) sum up for each input to your algorithm, continue it from where you left off.
• Store the value of the Euler-Mascheroni constant. To vastly more precision that you're going to get with this slowly convergent series: 0.57721566490153286060651209008240243104215933593994.
• Only take logs when you're going to output a sample to be consumed by your fitting algorithm.
• The Euler-Mascheroni constant part of the interpolation isn't the interesting bit; it's a constant.
• f() has an essentialy singularity at zero (due to the logarithm). So it's not precisely straightforward to attack analytically. However, taking the usual dodge, expanding around 1, gives coefficients that are values of the Riemann zeta function evaluated at successive integers. E.g.,

$f(x)=(1-\gamma ) (-2 {\frac {\pi ^{2}}{6}})(x-1) ({\frac {3}{2}}-\zeta (3))(x-1)^{2} (-{\frac {4}{3}} {\frac {\pi ^{4}}{90}})(x-1)^{3} ...$

and so these coefficients converge very slowly to zero, like 1/ln(n). Conveniently, they alternate, or the sum wouldn't converge.

• However, expanding f() around larger values, say 10, gives coefficients that decrease like 10^-n. This suggests that there are absurdly rapid numerical evaluation methods for large values of n. Which is surprising because f(n) converges to zero only like 1/P(n) where P is a function that grows slower than any polynomial.

Good luck. -- Fuzzyeric 03:17, 20 September 2006 (UTC)

Great, thanks for everything. -- Meni Rosenfeld (talk) 05:12, 20 September 2006 (UTC)

I'm feeling mildly embarassed for not remembering why it's called the Euler-Mascheroni constant... See Euler-Maclaurin summation formula. Applied to the partial sums of the harmonic series, this gives...

$f(n)=\ln {n} \gamma {\frac {1}{2n}}-\sum _{k=1}^{m}{\frac {B_{2k}}{2kn^{2k}}} \theta _{m,n}{\frac {B_{2m 2}}{(2m 2)n^{2m 2}}}\ ,\ 0\leq \theta _{m,n}\leq 1$.

This is a much faster way to evaluate f(n), but is only asymptotic; the Bernoulli numbers grow fast enough to exceed the denominator in the sum. The smallest term in the sum seems to occur around k = n/3. So this answers two questions (one of which you asked). First, the Euler-Maclaurin formula provides a method to attack sums of inverse powers. Second, this asymptotic formula should provide a very rapid way to numerically evaluate your sum to excessive precision. -- Fuzzyeric 02:22, 22 September 2006 (UTC)

Thanks! -- Meni Rosenfeld (talk) 06:19, 22 September 2006 (UTC)

thanks for the welcome

yes, sorry about the correction I made, I didn't understand it, I realised right after that I had made a mistake. And I don't know how to revert articles, so I left it.

what I was trying to say in my comment, is, that a trapezium is a shape with at least 2 sides parallel... I no longer have my Australian Math text book, but it explains it completely, with the diagram. —The preceding unsigned comment was added by Rkeysone (talk • contribs) ..

To revert an article, go to the article's history, click on the date of the version to which you wish to revert, then click "edit this page", then "Save page" (don't forget the edit summary!). Of course, you could also manually edit the article to remove what you inserted.

About the "normal" trapezoid, some authors write that it has at least a pair of parallel sides (which makes the most sense), but some authors (and I believe most) write that it must have exactly one pair. There isn't a universally accepted definition.

Don't forget to sign with ~~~~! -- Meni Rosenfeld (talk) 06:23, 25 September 2006 (UTC)

Dice probability

I was thinking that some elements of our discussion on the math reference desk would be useful if added to the probability section of Dice. Would you mind if I copied the math markup you wrote for that second formula (specifically,

<math>f(n,s,k) = \sum_{i=0}^{\left \lfloor \frac{k-n}{s} \right \rfloor} (-1)^i {n \choose i} {k-1-si \choose n-1}</math>)

for use in the article? —Saric (Talk) 00:21, 28 September 2006 (UTC)

Of course I wouldn't mind. In fact, I don't even have the right to mind, since the formula isn't mine (I've only written the markup for it, which is all in a day's work), and even if it was, everything I write here is under the GFDL. I think it will be a nice addition to the article. -- Meni Rosenfeld (talk) 08:23, 28 September 2006 (UTC)

Reverting

Sorry for reverting to an unclean version on square root. I think I thought "von eduard" was the name of the function. Excuse my ignorance. Itsmejudith 10:38, 11 October 2006 (UTC)

No problem. It just looked weird to me to revert one of that user's edits and not the other. Also, this kind of revert can be dangerous, since people are less likely to check the recent history if they see the last edit was a revert by an established user, and thus the poor edit might stay for a long time (I saw a case recently where an obvious vandalism stayed for 10 days because it was overlooked among other edits made at that time). But no harm done. -- Meni Rosenfeld (talk) 11:39, 11 October 2006 (UTC)

Today's featured article

Just wanted to let you know a featured article you worked on, 0.999..., was featured today on the Main Page. Tobacman 00:31, 25 October 2006 (UTC)

Great, thanks for the info! -- Meni Rosenfeld (talk) 19:59, 26 October 2006 (UTC)

Troll warning

Thanks for the info about Mr Troll, I will ignore him from now on. Your work on the 0.999... discussion is great and very helpful. I'm sorry if I've been annoying ranting about how we should give more emphasis to number systems that make use of infinitesimals. It's mainly just that I remember years ago, when they taught me this at school how it annoyed me, so perhaps I feel too sorry for people in a similar position. Besides, I feel like the intuition is very interesting and has some relevance and a kind of correctness in other areas. Anyway, thanks for your patience.

(copied to User talk:157.161.173.24) -- Meni Rosenfeld (talk) 15:16, 27 October 2006 (UTC)

Hey, thanks for all your efforts on 0.999... and the discussions thereof. I wanted to ask you, is there anything we can do to get this troll blocked from the Arguments page? He really is disrupting the discussion to a serious degree, and I'm losing interest in helping with it because of him. It is sad to think of people leaving the article knowing less than they could, because of all his crap. What can we do about it? Maelin 13:53, 29 October 2006 (UTC)

Hi. I'm not too sure about the possibilities, or about whether trolling is sufficent grounds for blocking (and it will be hard to convince anyone that he is trolling, since you really have to understand what is going to realize it). In any case, you should probably bring this up at WP:ANI where someone will probably be able to help. I'm unfortunately rather busy right now, but in the weekend I'll try to do some damage control. Good luck until then. -- Meni Rosenfeld (talk) 11:08, 31 October 2006 (UTC)

Hello Maelin, Meni. I wanted to block the troll, but s/he was already blocked due to vandalism of acid rain. Unfortunately, blocking an IP address often has no effect, but let's hope that it helps. -- Jitse Niesen (talk) 11:59, 31 October 2006 (UTC)

"Mathematics of the real numbers"

There most certainly is a "mathematics of the real numbers", in the same way that there is a "mathematics of the hyperreal numbers" or a "mathematics of the transfinite cardinals". The fact that 0.999... = 1 is a direct consequence of the structure of the real numbers, and does not necessarily hold for the similarly-named objects in other axiomatic systems. The properties of sums of infinite series, and the absence of infinitesimals from the standard reals, are not intuitively obvious; hence all the controversy about this small, but crucial result. -- The Anome 10:48, 28 October 2006 (UTC)

Continued at Talk:0.999... -- Meni Rosenfeld (talk) 16:02, 28 October 2006 (UTC)

12/0 = 0?

Since you participated in the discussion at talk:division by zero about the chart being sold by an (allegedly) educational publisher that says that 1/0 = 0, 2/0 = 0, etc., perhaps it will interest you to know that at this web site where the chart is sold, the publisher now solicits opinions of the product. You can go there and tell them what you think. Michael Hardy 20:56, 9 November 2006 (UTC)

Thanks for the info, will do. -- Meni Rosenfeld (talk) 21:11, 9 November 2006 (UTC)

Hi Meni - did you ever submit a comment on this chart? I just looked at it and there were no comments shown (so I added one). I guess they still have a lot of stock to get rid of.... AndrewWTaylor (talk) 21:57, 4 January 2008 (UTC)

I recall trying to and getting to some sort of error page. I figured back then that someone has beat me to it and they have already discontinued its sale, thus its comment page being unavailable. That was wishful thinking, apparently. -- Meni Rosenfeld (talk) 23:06, 4 January 2008 (UTC)

I looked there and couldn't see your comment, so I tried my luck as well. I see now they are claiming to publish it within 2 business days - we'll just have to wait and see. -- Meni Rosenfeld (talk) 23:17, 4 January 2008 (UTC)

Great post

Hi. Great post there on Talk:0.999.../Arguments#Let's end this madness ("John: Okay, I'll try this one more time.")! --Kprateek88(Talk | Contribs) 12:04, 10 November 2006 (UTC)

Thanks, I tried to make it one :-) Unfortunately, I have made some posts in the past which I think were rather good, but seemed to have little effect :( -- Meni Rosenfeld (talk) 12:09, 10 November 2006 (UTC)

Disappointed in Square Root Methods page...

Meni -

First, I want to thank you for the obvious time and effort you spent editing/maintaining this subject.

Second: I wanted to express my concern over your decision to remove other methods of calculating an initial estimate (ref 10:55, 8 September 2006). (I am sorry I have not replied sooner - I made some edit back in May 2006 and stored a copy of the page for my reference and had not returned to this WP page until now.) I have long developed software for embedded applications with both processor and real-time limitations. The type of estimation that was described was very useful as an initial seed for a Newton's method iteration on an reciprocal square root algorithm (which, as the page correctly states, can require a fairly accurate seed value to converge). The only (rough) estimation technique currently left on the page is, by comparison, grossly inaccurate, as it omits the correction factor. Also, the one you deleted is valuable for processors and applications where divisions are too costly to consider.

A third note: Rather than merely being a means of finding a square root, the reciprocal square root is extremely important for direct use in very fast normalization/rescaling of L2 vectors (by a single multiply). For this very common use, it is vastly superior to directly finding and using the square root, especially in cases where there is no hardware support for division.

And lastly: As for the basis upon which I tweaked the adjustment factors (my edits of May 2006), I explicitly wrote how I derived the adjustment factors: "where the derivation of the adjustment is the average of the square root of first digit and the square root of the first digit incremented by one, all divided by √10." Put another way, the adjustments were spaced to minimize the maximum errors generated on each interval --- for a leading digit of 1 on the interval of [1,2) I used the midpoint of the function's interval of [1/SQR(10), SQR(2)/SQR(10)). I believe I had made a study of this technique at the time, and found the theoretical values I had provided in WP were correct & superior to the original values when supported by a large sample set of calculations. For my use I needed to fully comprehend the underlying concept, as I was hoping to characterize/implement it for a moderately larger binary sized table, not one with just 9 (decimal) entries. Plus I needed to adapt it to RECIPROCAL square root estimation. Once I analyzed what was being shown, I recognized it as a simple table based technique I had commonly implemented in the past. —The preceding unsigned comment was added by 63.241.173.64 (talk) 23:08, 24 January 2007 (UTC).

I understand you mean this. My reason for this edit was very specific, as I expllained in the edit summary - it is identical to taking one step of the Babylonian method, which is already described in the article. ${\sqrt {N^{2} d}}\approx N {\frac {d}{2N}}$ when $d\approx 0$ is just another way of writing ${\sqrt {S}}={\frac {1}{2}}(x {\frac {S}{x}})$ when $x\approx {\sqrt {S}}$. As for the importance of making such a step before starting to use reciprocal root methods, I have added a note to that effect to the reciprocal methods section. I hope you will be satisfied with the current version. -- Meni Rosenfeld (talk) 18:44, 25 January 2007 (UTC)

Mathematics CotW

Hey Meni, I am writing you to let you know that the Mathematics Collaboration of the week(soon to "of the month") is getting an overhaul of sorts and I would encourage you to participate in whatever way you can, i.e. nominate an article, contribute to an article, or sign up to be part of the project. Any help would be greatly appreciated, thanks--Cronholm144 23:28, 13 May 2007 (UTC)

Thanks for the information. -- Meni Rosenfeld (talk) 16:13, 14 May 2007 (UTC)

Happy Birthday

Just a happy Birthday message to you, Meni Rosenfeld, from the Wikipedia Birthday Committee! Have a great day!

Politics rule 23:13, 14 May 2007 (UTC)

Thanks! Two days ahead of schedule, but I guess that works too :-) -- Meni Rosenfeld (talk) 08:16, 15 May 2007 (UTC)

Happy Birthday!

Just a happy Birthday message to you, Meni Rosenfeld, from the Wikipedia Birthday Committee! Have a great day!

GrooveDog 01:21, 16 May 2007 (UTC)

Wishing you all the best on your birthday! From the Wikipedia Birthday Committee.

Whatever you wish for on your special day,

May each of your wishes come true.

Cheers, PeaceNT 15:09, 16 May 2007 (UTC)

Thanks! -- Meni Rosenfeld (talk) 17:20, 16 May 2007 (UTC)

Gbgg89

I appologise for the impoliteness, I just hadn't checked my refference question for a while, and I guess I just let them pile up. Sorry! I'll be more carefull in the futer! Gbgg89 02:23, 13 June 2007 (UTC)

Ref desk analysis

I didn't think so, but I just love that name, "Caratheodory" .... ;-) iames 19:39, 13 June 2007 (UTC)

lol. Myself, I am only familiar with Carathéodory's theorem (convex hull), though I now see there are plenty Carathéodory's theorems. -- Meni Rosenfeld (talk) 19:44, 13 June 2007 (UTC)

WP:RD/Math

We always look forward to your clever posts and this is an excellent example. ;-) - hydnjo talk 00:48, 30 July 2007 (UTC)

Clever posts? Me? Nah, I just keep the OP busy until someone like KSmrq or Lambiam provides a real answer :) -- Meni Rosenfeld (talk) 07:50, 30 July 2007 (UTC)

With reference to your interpretation of square roots

While I appreciate your opinion that only half of the square roots in the world matter, the “most texts” you refer to are undoubtedly written for those who understand very little about the consequences of having multiple roots to an equation. One example, from an engineering standpoint, is that some machines operate differently in the forward direction than the reverse. For instance, the shock absorbers on a car are angled to the front of the vehicle. As non-symmetrical elements, they operate differently when expanding than contracting, and are positioned to provide a critically damped experience when the car moves in the forward direction. If one drives in reverse over a speed bump, the impact is significantly more forceful. Try it!

Your point that “most texts refer to...” is actually the one that isn’t meaningful. Your point refers to your personal philosophy that only principle square roots are meaningful. The mathematical actuality is that both roots matter, and this equation is a perfect example of why. It will very much be to your benefit in your continuing education if you realize that math works, not just your perception of what is an appropriate convention.

Best, Dr. Gnow. Dr gnow 05:52, 31 August 2007 (UTC)

You haven't read my comment (or the article square root, for that matter) carefully enough. I have not implied that only one square root matters, but rather that only one is denoted ${\sqrt {x}}$ (with the other, equally important root, being denoted $-{\sqrt {x}}$). You only have any sort of guarantee that "math works" if you are careful with your notation, otherwise you can quickly end up with absurdities. Writing "${\sqrt {1}}=\pm 1$" is not meaningful since $\pm 1$ is a shorthand for something else, not an object in itself; "${\sqrt {1}}=1$ and ${\sqrt {1}}=-1$" is absurd, since equality is transitive and $1\neq -1$. This doesn't mean that you must accept the ${\sqrt {1}}=1$ convention, but you must accept some convention if you want anything you do to be meaningful. One alternative is ${\sqrt {1}}=\{1,-1\}$, which is consistent but of dubious utility.

I have no idea whatever gave you the impression that I have a "personal philosophy that only principle square roots are meaningful" or that I "understand very little about the consequences of having multiple roots to an equation" (yes, I have taken this out of context but I have no doubt this is what you had in mind). Frankly, I am offended by these conclusions. -- Meni Rosenfeld (talk) 10:24, 31 August 2007 (UTC)

roots, continued

The “dubious utility” from your previous post is the reason that the original equation in question is internally consistent. It is the convention of considering only primary root of 1 that leads to what appears an inconsistent equation. You are correct that equalities are transitive, then you go on to make the same mistake I previously pointed out by using only one root on each side of the equation.

Claiming that I did not read the article or your post reflects your perception that as we disagree, your opinion is somehow more valid than mine. It is you who completely missed the point of my original post.

Also, if you choose to be offended so easily, perhaps you should not refer to the contribution of others as “not really meaningful.”

Dr gnow 19:53, 31 August 2007 (UTC)

This discussion is clearly not taking us anywhere. Have a good day. -- Meni Rosenfeld (talk) 20:01, 31 August 2007 (UTC)

Wow, Meni. If you feel like you hadn't been stomped to the appropriate level, the square root page has been updated to reflect my point. Its almost like you need to read the page again, not me. How weird is that? Its almost like, I don't know, you are stuck in your mind frame and don't appreciate new information? Just a thought. —Preceding unsigned comment added by Dr gnow (talk • contribs) 05:34, 3 September 2007 (UTC)

Wow.

Just, wow. You have huge, gigantic balls. I can't believe that you have actually tried to make an argument with such circular logic and such an authoritative voice, then you play the "I can't see you" card by claiming our discussion is going nowhere. How arrogant of you.

If you're really that unable to follow through with a discussion, please remove your comment from my post on the square root page. Also, I think it would benefit you to put quite a bit more thought into what you put on Wikipedia, it's fairly permanent way to document your work. I don't particularly like or respect you, but I'd still hate to see your quest for self importance injure your career later in life.

Best. Oh, and why don't you write "convention" one more time? Again, your "convention" clearly doesn't apply here, but you seem to enjoy writing the word.

Dr gnow 05:19, 1 September 2007 (UTC)

Protect the faith!

Meni,

   Thank you for defending the REAL WORLD from the witchcraft of the AMERICAN SCIENTIST.  How dare he claim that there are two answers to a factual question?   The Lord advises us on difficult questions, and I'm glad he's spoken to you and shown you THE WAY in this matter.  Its best that you ignore that rapscallion, Jesus wouldn't respect you if you entertained his nonsense.  I don't think you're arrogant, I think you walk in the path of the Lord, even if, as a Jew,  you don't yet appreciate the grace of Jesus.  Nobody should hold that against you in the context of math and science.

JesusLuver247 05:44, 1 September 2007 (UTC) JesusLuver247, You're way off the mark. I hope that even someone like Meni can put you back on track, and I really hope that your zeal and self conviction in a field you don't understand invites Meni to reconsider his self-biased conclusions. Just like Meni, you need a wider perspective before you comment on these issues.

Best, Dr gnow 05:56, 1 September 2007 (UTC)

Thanks for your help with .999...

I really appreciate it. The soon to be registered unanonymous user ;) . —Preceding unsigned comment added by 205.161.125.254 (talk) 20:13, 4 September 2007 (UTC)

No problem :-). It is also worth noting that registering is easy, it really shouldn't take more than half a minute... -- Meni Rosenfeld (talk) 20:19, 4 September 2007 (UTC)

Barnstar

I don't know if I deserve that, as I haven't been really active in the help desk lately... But thanks, I've put it in my user page. -- Meni Rosenfeld (talk) 11:04, 5 September 2007 (UTC)

My new page

Hello again, I've spent some time editing on my page and have included (though not yet complete) one of my more significant/useful works relating to polynomials. Feel free to check it out. A math-wiki 05:33, 11 October 2007 (UTC)

Hi, thanks for the info. Looking at it suggests that your overall goal is "Given a polynomial $p(x)$, find those values of $x\in \mathbb {C}$ for which $p(x)\in \mathbb {R}$, and the behavior of the polynomial at those points". However, I feel that such an objective sort of defeats its own purpose, since if we are interested in complex inputs, we should be interested in complex outputs as well. Also, for quadratics the behavior displayed is fairly trivial, and for higher degrees it seems too difficult to pinpoint any specific behavior. I don't deny that there is an elegant symmetry in the quadratic case, but nothing too deep, really.

If you do wish to investigate this further, though, what you probably need is a good CAS. The only one I have real experience with is the proprietary Mathematica, which is powerful but expensive, but there are some free ones as well (see, for example, Comparison of computer algebra systems). -- Meni Rosenfeld (talk) 12:23, 11 October 2007 (UTC)

I was only really interested in looking at the graphincal behavior of complex solutions for different polynomials, so restricting the output to real values is of no real consequence. A math-wiki 00:01, 18 October 2007 (UTC)

Sorry

Yeah I got a little over my knowledge level their on the paths question in the refence desk. I think I have the algorithm he's looking for now. A math-wiki 00:01, 18 October 2007 (UTC)

It's no problem really. I am only keeping in mind the observation that sometimes, a misleading answer can be worse than no answer as all. Obviously I make mistakes myself, but I try to keep those at a minimum. -- Meni Rosenfeld (talk) 08:58, 18 October 2007 (UTC)

Block Matrices

Thanks for helping me with the block matrices. I am still not absolutely sure about the proof yet. Since the page has been archived I was wondering whether you could take a look at the proof that I have written here and help me finish it. Again thanks--Shahab 04:13, 20 October 2007 (UTC)

Division by zero

I've requested semi-protection for Division by zero and Theory of everything. — Loadmaster 23:29, 25 October 2007 (UTC)

I think blocking the IP range 129.138.20.01111xxx would have been more effective, but that should work, too. Thanks for the info. -- Meni Rosenfeld (talk) 11:21, 26 October 2007 (UTC)

Conflicting positions

I noticed in couple instinces that our answers for some of the questions asked on the reference desk have been at odds. I want to preempt any bad blood. I find it occasionally worrysome that you sometimes give answers that are quiet possibly well beyond the understanding of the OP. Such answers aren't wrong, but are generally not that helpful nor are they what the OP is really looking for. If want to point out that their question relates to somethings they as yet may not understand that's ok but try if at all possible to answer there question at the same level as it was asked. I took me several years before I learned how not confuse people I tried to help in math class. Keeping your explanations on par with someone's understanding is not always that easy! It usually translates to giving through explanations for anything that is even slightly beyond their appearant understanding it is necessary to give a clear answer to their question. A math-wiki 09:02, 14 November 2007 (UTC)

I do make a conscious effort to keep my replies at a level the OP can understand (do not confuse this with occasions when I am responding to a different issue raised in the discussion, and not directing my comments at the OP). If you have any specific example where you think my effort has failed, please mention it so I can take it into the consideration.

As long as we are giving gentle criticism on each other's contributions, I would like to mention a worrysome trend in your contributions as well. All too often you make comments about topics which are, as it seems, beyond your understanding. What's worse, you often use a tone which is too authoritative, hiding the fact that you are basically speculating. This can be misleading to the OP and other readers, and annoying to more knowledgeable people whose answers you contradict. I suggest the following: Before you post a reply, take a look at Wikipedia articles about related topics, and see if they match what you have thought. Then, think really hard if you are truly confident about your response, and if it really provides new insight. Only then write your comment in a tone which reflects your evaluation of your own understanding of the subject. If you are not sure, write your thoughts as a question which others can answer. Doing so can guarantee a long and successful career as a RefDesk regular, sharpening your knowledge and understanding in the process; If you fail to do so, do not be surprised if people bash your contributions. -- Meni Rosenfeld (talk) 13:07, 14 November 2007 (UTC)

I will keep that in mind, I suppose a good example would be mention in the imaginary number question about i and -i, yes you are right that the distinction is arbitrary but mentioning field theory to someone who is probably a high school Junior or Senior is basically a waste of text, even if it might be useful to some of the others who are answering. If you feel it is still necessary to reference something like that well beyond the OP's understanding try adding an explanation of at least the ideas behind it. I should also mention that people like our OP here sometimes are not very proficient with mathematical terminology and might miss interpret from your tone that arbitrary meant that it was impossible to distinguish between i and -i, implying it does matter if you write i or -i and that they are freely interchangable, which I am pretty sure is not correct. I should also note when I feel that a correction to someones answer in order I usually try to kritique the person's answer, being extremely specific as to what is completely correct and what is misleading or not correct. A math-wiki 23:41, 14 November 2007 (UTC)

Note that I have never mentioned fields in that response (are you perhaps mistaking me for Gandalf?), though they were to some degree implied. Note also that none of my posts in that thread where directed at the OP - the first was addressing what I saw as an error in Salix's reply, the second was a direct answer to Salix's question, and the rest were addressed to you. Correspondingly, in all cases, I did not try to write in a way the OP should understand - but I still think in retrospect that the OP should be able to at least get the general idea (even though we know very little about him - he only posted one, rather cryptic, question). -- Meni Rosenfeld (talk) 09:23, 15 November 2007 (UTC)

Thank you

Thank you for being able to calmly say what I was getting too upset to say! I have been hugely heartened by the response of so many Wikipedians to the difficulties recently, it really means a lot to me. Thanks again, and best wishes, DuncanHill (talk) 17:46, 21 November 2007 (UTC)

You're quite welcome, I'm glad to have been able to lift your spirits a little bit. -- Meni Rosenfeld (talk) 17:55, 21 November 2007 (UTC)

Hey, thanks!

Thanks for helping me in the Help:Reference Mathematics section. My math teacher isn't so good, and just gives our class worksheets to do on ourown without explaining how to do them. Then they turn to me to tutor them and teach them how to do it. It's so much easier when someone older explains it out and gives assistance, instead of everyone just expecting me to know what's going on. Thanks again, S♦s♦e♦b♦a♦l♦l♦o♦s ^{(Talk to Me)}

No problem. Remember, the best way to fully understand anything is to teach it to others, so you should be glad whenever someone asks you for guidance and gives you such an opportunity. I'm sure your teacher would also be glad to answer any questions you might have (he\she can't be that bad, right?). -- Meni Rosenfeld (talk) 22:08, 4 December 2007 (UTC)

Are you sure? He doesn't answer questions, just points to a Dictionary! A Dictionary! That's why everyone asks me because I get it faster. If I learn one strategy, I learn it and manipulate it (Correctly) to work for all of the stuff. Because I'm smarter, the teacher piles on extra homework at a higher grade level and says: "Do it. It's due tomorrow." That's the stuff that I need help with. S♦s♦e♦b♦a♦l♦l♦o♦s ^{(Talk to Me)} 22:34, 6 December 2007 (UTC)

Oh well. Good luck, then. -- Meni Rosenfeld (talk) 10:55, 7 December 2007 (UTC)

Division by Zero, (uses of)

(I see you have many similar headings on your talk page)

but anyway, you mentioned something about uses for the division by zero.

What could they possibly be, we're not even talking about something in the real number line?

and thanks for the correction about the math book thing. Freenaulij (talk) 03:11, 6 December 2007 (UTC)

I wouldn't be able to explain them too well. I can suggest taking a look at Riemann sphere, though it is slightly advanced. Another example is in making theorems like the root test for power series more elegant - If we agree that 1/0 = ∞ and 1/∞ = 0, we can formulate it as saying that the radius of convergence of $\sum a_{n}z^{n}$ is ${\frac {1}{\lim \sup {\sqrt[{n}]{|a_{n}|}}}}$ without any additional words. -- Meni Rosenfeld (talk) 16:18, 6 December 2007 (UTC)

My limit at the Math RD

I've replied to your answer. Yes, I meant that (with the absolute value), forgot to type it, but it still doesn't work, why? --Taraborn (talk) 17:19, 31 December 2007 (UTC)

Replied there. -- Meni Rosenfeld (talk) 18:04, 31 December 2007 (UTC)

2-Dimensional limit

Just felt like dropping some aditional lines to my apologies at the RD. You are right in that my posting there today was appalling. But I give you my word that no offense was intented. I'll try next time to be more precise and cautious before giving an answer. Regards, Pallida  Mors 19:06, 7 January 2008 (UTC)

Don't worry about it. I wasn't that offended at the personal level, and I don't think anyone else was - I just felt your hastiness wasn't very proper, and is something to be mentioned and kept in mind in the future. -- Meni Rosenfeld (talk) 19:15, 7 January 2008 (UTC)

Domain name and email without hosting needs

Thanks for the info for my inquiry on wanting a domain name and email without needing hosting. I looked more at your list of 10 and you are right there are better options. I set up a Bluwiki to help with my decision making here: http://www.bluwiki.com/go/Domain_and_email. Guroadrunner (talk) 11:45, 17 January 2008 (UTC)

No problem. Note that register.com offers domain registration for 35$/yr, and Go Daddy offers domain registration for 3$-10$/yr, depending on TLD. -- Meni Rosenfeld (talk) 11:57, 17 January 2008 (UTC)

Trolls?

Greetings. I noticed that you were perhaps on the receiving end of some possibly negative comments from some anonymous trolls on the mathematics reference desk. Just wanted to advise you not to put up with it (warn and report where necessary) and also consider just removing stupid comments and not replying to them. Perhaps I'm making too much of this, but it just annoyed me that you are trying to help people with attitudes like this. Regards, MSGJ (talk) 14:04, 29 January 2008 (UTC)

Well, technically, only my first post in that thread was meant to directly help - the others were meant to criticize the inappropriateness of anon's behavior (which could also be seen as a sort of help). There are many ways to deal with trolls, and the "best" way depends on the people on both ends. In this case, I don't see how any kind of reporting can be helpful - only a few posts were made, and the person uses at least 3 IPs (assuming 81.215.240.54, 85.98.176.72 and 78.171.57.143 are the same) so blocking will not be effective. Ignoring is certainly one way. Removing is another, as Gandalf61 had done to this. But I feel the best response for me here is to simply ridicule the troll. It's certainly more fun, and he seems like the type that will quickly give up when he sees he is not taken seriously. -- Meni Rosenfeld (talk) 14:30, 29 January 2008 (UTC)

Clustering

Hi Meni, Hope I didn't disillusion you too much about computer vision and clustering. Anyway I had a though about possible datasets. What about using data collected from wikipedia? Its a vast source of data with lots of revision/contribution histories, internal linking and such like. Not quite sure how you would get a Euclidean metric out of it though.

The other thing to try is to ask around your university, There are probably people there in all sort of disciplines with handy datasets. --Salix alba (talk) 15:52, 3 February 2008 (UTC)

Well, having seen that this particular line of research (investigating real-world databases) isn't going to be as easy as I hoped, I've put it on the back burner for the time being. It seems to me that processing Wikipedia-based data would be even more troublesome than processing images, but it is certainly something to be considered should all else fail. While there are definitely people around dealing with all sorts of data, I suspect that it will not be easy to find anything immediately usable by me - but it's worth a try. Thanks. -- Meni Rosenfeld (talk) 16:15, 3 February 2008 (UTC)

Very late reply to your message on my user page: "WP:SOCK"

You wrote: You may want to look at this regarding some of the question raised on the userpage. Basically, you should be okay as long as you don't use sockpuppetry for evil and don't use both accounts to participate in the same (or related) articles\discussions. -- Meni Rosenfeld (talk) 17:09, 27 January 2008 (UTC)

Thanks for your concern! No, I certainly won't participate in the same discussions as my "master's hand", and I will hopefully stay away from all vain and unfriendly discussions, vandalism or other evil things anyways. ... And sorry for the late reply as I'm not being used unless my "master's hand" needs me for some silly questions... (oh, what a life!)... --Thanks for answering (talk) 17:30, 21 March 2008 (UTC)

Mathematics Desk

$F\left(n\right)=\sum _{k=0}^{2^{n}}{\frac {\left(-1\right)^{k}\left(nx\right)^{2k}}{\left(2k\right)!}}$ should work. -- Meni Rosenfeld (talk) 17:37, 12 April 2008 (UTC)

Thanx, but unfortunately, you haven't proven that for every real interval there is a natural number n such that F(n) has a root in the interval. Eliko (talk) 19:28, 12 April 2008 (UTC)

Continued there. -- Meni Rosenfeld (talk) 08:24, 13 April 2008 (UTC)

OK. Let's continue there. Eliko (talk) 11:14, 13 April 2008 (UTC)

Thanks

Thanks for your quick response! —Preceding unsigned comment added by 68.99.185.240 (talk) 23:26, 10 May 2008 (UTC)

No problem. -- Meni Rosenfeld (talk) 23:33, 10 May 2008 (UTC)

Happy Birthday

Just a happy Birthday message to you, Meni Rosenfeld, from the Wikipedia Birthday Committee! Have a great day!

Meldshal42_{Hit me}^{What I've Done} 19:26, 16 May 2008 (UTC)

	Happy Birthday	from the Birthday Committee
	Wishing Meni Rosenfeld a very happy birthday on behalf of the Wikipedia Birthday Committee! Don't forget to save us all a piece of cake!

Idontknow610^TM 20:28, 16 May 2008 (UTC)

Happy birthday fellow Wikipedian!

The Wikipedia Birthday Committee wishes you a very happy birthday! Enjoy your special day.

Best wishes from Canada!  ;-) --RobNS 02:35, 17 May 2008 (UTC)

Invalid division proposition

There is a reply to your comments at Invalid division proposition at Fuzzyeric's Talk. —Preceding unsigned comment added by Fuzzyeric (talk • contribs) 22:34, 17 May 2008 (UTC)

Pong. -- Fuzzyeric (talk) 23:17, 17 May 2008 (UTC)

Nash

Hi Meni, I replied to your Nash equilibrium question on the archive page of the maths reference desk. Not sure if it's at all relevant, but I wanted to point it out anyway. Oliphaunt (talk) 10:41, 28 May 2008 (UTC)

Thanks. -- Meni Rosenfeld (talk) 12:06, 28 May 2008 (UTC)

You guys

Gandalf61 and Algebraist and Lambiam and KSmrq and Meni Rosenfeld and others have taught me more about mathematics than have all of my formal instructors - THANKS. hydnjo talk 02:56, 28 December 2008 (UTC)

Thank you for your kind words, and you're welcome! Sorry for the late reply. -- Meni Rosenfeld (talk) 15:28, 19 May 2009 (UTC)

new WP:RDREG userbox

This user is a Reference desk regular.

The box to the right is the newly created userbox for all RefDesk regulars. Since you are an RD regular, you are receiving this notice to remind you to put this box on your userpage! (but when you do, don't include the |no. Just say {{WP:RD regulars/box}} ) This adds you to Category:RD regulars, which is a must. So please, add it. Don't worry, no more spam after this - just check WP:RDREG for updates, news, etc. flaminglawyer^c 22:13, 6 January 2009 (UTC)

Al Farooj Fresh

Hi Meni, I came to your page after searching for users with knowledge of Arabic. We are discussing Al Farooj Fresh at AfD and I think it's close to being notable with English language sources, however it's probably not quite there. I wonder if you could have a look for relevant Arabic sources and bring them to the party please?! Thanks, Bigger digger (talk) 12:34, 19 May 2009 (UTC)

I am afraid my knowledge of Arabic is insufficient to contribute in any meaningful way. Sorry. -- Meni Rosenfeld (talk) 15:25, 19 May 2009 (UTC)

Thanks for letting me know. Cheers, Bigger digger (talk) 15:56, 19 May 2009 (UTC)

Wellcome back!

Long time no see at the reference desk. Really nice to see you're back! Wellcome! NorwegianBlue ^talk 18:33, 27 May 2009 (UTC)

Thanks, it's good to be back. -- Meni Rosenfeld (talk) 20:39, 27 May 2009 (UTC)

Why there's no "empty average"

The other answers given appear correct, but here's a more concrete way of looking at it:

Say we're measuring heights above sea level, and you get 0, 1, and 5 (after measuring the heights at high tide). Your average is (0   1   5)/3 = 2 feet above sea level. I measure the heights at low tide when the water is 4 feet lower, so I get 4, 5, and 9. My average is (4   5   9)/3 = 6 feet above sea level. You got 2 feet. I got 6 feet, when the water is 4 feet lower. So we BOTH got the same average height. But if it were correct to say the average of 0 numbers is 0, then should that 0 be your sea level, or mine? There's no non-arbitrary answer. So it doesn't make sense to say the "empty average" is 0. Michael Hardy (talk) 23:42, 23 June 2009 (UTC)

Thanks! -- Meni Rosenfeld (talk) 08:56, 24 June 2009 (UTC)

Card games

Thanks for spending so much time on my Reference Desk question! A pity that it's such a ridiculously hard question; I never imagined that it would be virtually impossible to answer. Nyttend (talk) 12:21, 10 July 2009 (UTC)

You're welcome! Note that it may still be possible to find an estimate, by running a simulation with a strategy that is "close enough" to perfect. -- Meni Rosenfeld (talk) 12:52, 10 July 2009 (UTC)

Thanks!

Dear Dr. Rosenfeld:

I was the person asking the Bernoulli trials. Thanks for your response! Your solution is excellent, I found it very educational.

70.29.26.221 (talk) 14:34, 15 July 2009 (UTC)

No problem. Sadly, I'm not a Dr. yet. -- Meni Rosenfeld (talk) 20:06, 15 July 2009 (UTC)

I'm sure you will be someday. 174.88.242.12 (talk) 14:12, 18 July 2009 (UTC)

Base pi

Dear Meni, I have a small curiosity raised by a recent thread. At a certain point they mentioned a representation of real numbers in base π. I understand it as writing a number as a series of decreasing powers of pi: but where do we pick the coefficients? A minimal set should be {0,1,2,3} although it gives non-unique representations. Is it just this, or is there something more subtle? Is there a standard form for this representation, like the one you mentioned for the golden ratio base? (Ah I see, there is a maximal one...) Do not loose too much time to answer my question. I'm just shy about putting the question there because it seemed a kind of hot topic and I do not want to stir up troubles... Thanks, Pietro --pma (talk) 13:01, 28 August 2009 (UTC)

I'm no expert on this, but basically the coefficients should indeed be in {0, 1, 2, 3}, and for a unique representation you choose the one where the most significant digits are as large as possible (which I think is what you meant by "a maximal one"). So the "canonical" representation of 4 in base π would be "10.220122..." rather than "3.30110211...". I think that for an algebraic base which solves a polynomial with coefficients less than itself (like phi), you will be able to express this constraint in a more elegant way (for most cases anyway; the generic constraint automatically prefers terminating expansions to their duplicates, while the specific ones may not); for transcendental bases I don't think this is possible. -- Meni Rosenfeld (talk) 13:51, 28 August 2009 (UTC)

Thanks! --pma (talk) 14:01, 28 August 2009 (UTC)

Evaluating a probability estimator

Hello Meni

Is your problem asked on Wikipedia:Reference desk/Mathematics#Evaluating a probability estimator solved?

Bo Jacoby (talk) 06:46, 8 September 2009 (UTC).

Not completely. The link you have provided is certainly relevant, but I'm not sure how to adapt it to my particular case. Anyway, I think the approach I suggested will satisfy me for now. Sorry for not replying - I was waiting to hear more suggestions. -- Meni Rosenfeld (talk) 18:38, 8 September 2009 (UTC)

I am not sure I understood the problem right. If it can be explained by means of a small example perhaps you get more suggestions. Bo Jacoby (talk) 12:21, 10 September 2009 (UTC).

Thanks. Unfortunately, I cannot disclose the particular problem I have, and I'm hard pressed to think of a different example or a better explanation. -- Meni Rosenfeld (talk) 19:43, 10 September 2009 (UTC)

Please Stop!

I am perfectly within my rights to delete any or all of the contents on my talk page. It is not rude in the slightest. I don't feel that your comments in any way add to the quality of Wikipedia or to my article editing; so they have been removed. This is a right that I intend to exercise for a third time. As for your comment "If you wish to remove this post you are within your right, but in this case do not expect me to ever communicate with you again." Well, to be honest, I would be very pleased if you were to stop communicating with me. (Although whether giving lectures is really communication is debatable.) In the last few weeks, you have made five unsolicited posts on my talk page about topics which do not involve you directly. If the parties involved have accepted my attempts to make peace (see here) then I don't see why you should keep writing condescending messages almost 24 hours after the event. Why can't you just let it drop? I would ask you not to post anything more on my talk page with regard to this matter since all parties involved see the matter as closed. If you continue to add similar posts after I have deleted them then I shall view your action as harassment. Please stop! ~~ Dr Dec (Talk) ~~ 20:23, 8 September 2009 (UTC)

Amusing. Tan | 39 20:43, 8 September 2009 (UTC)

I know, we live and we learn from our mistakes. ~~ Dr Dec (Talk) ~~ 20:57, 8 September 2009 (UTC)

To anyone who stumbles upon this page and is wondering what the fuss is all about, see my original attempt to reason with User:Declan Davis. After he has assured me that there was nothing to worry about, his continued behavior (evidenced everywhere in WP:RD/math) demonstrated that in fact there was. He then refused to accept any criticism and deleted my posts here, here and here. Now that I am convinced beyond any doubt that User:Declan Davis is a troll with no desire to amend his ways, I will be delighted to honor his request to cease my attempts to help him. I hope others will follow. -- Meni Rosenfeld (talk) 04:55, 9 September 2009 (UTC)

Update: The above links no longer work. -- Meni Rosenfeld (talk) 21:21, 12 October 2009 (UTC)

באשר לשאלתי בדסק המתמטיקה על פתרון אלגברי למשוואה בעלת ששה ביטויי-שורש

כמובן שכל הדיון אינו מתיחס למצבים טריויאליים, כגון למצב שבו אחד מביטויי-השורש שבאחד מאגפי המשוואה - זהה במקדמים שלו לאחד מביטויי-השורש שבאגף השני, או כאשר היחס שבין שני המקדמים שבאחד מביטויי-השורש - זהה ליחס הזה באחד משאר ביטויי-השורש. וכעת, לגופו של ענין: כזכור, אתה טענת שכשיש יותר מארבעה ביטויי-שורש אז כבר אין דרך [אלגברית] לפתור את המשוואה. ובכן, אני בכוונה בחרתי משוואה עם ששה ביטויי-שורש ולא עם חמישה, שכן יש מקרים - לא טריויאליים - שבהם כן ניתן לחלץ באופן אלגברי את פתרונה של משוואה בעלת חמישה ביטויי-שורש (מה שאין כן כשבמשוואה ששה ביטויי-שורש). לדוגמה

${\sqrt {2x 4}} {\sqrt {2x 2}} {\sqrt {x-1}}={\sqrt {4x 2}} {\sqrt {x 3}}$

לכן

$(2x 4) (2x 2) (x-1) 2{\sqrt {(2x 4)(2x 2)}} 2{\sqrt {(2x 4)(x-1)}} 2{\sqrt {(2x 2)(x-1)}}$ $=(4x 2) (x 3) 2{\sqrt {(4x 2)(x 3)}}$

לכן

$(5x 5) 2{\sqrt {(2x 4)(2x 2)}} 2{\sqrt {(2x 4)(x-1)}} 2{\sqrt {(2x 2)(x-1)}}$ $=(5x 5) 2{\sqrt {(4x 2)(x 3)}}$

לכן

${\sqrt {(2x 4)(2x 2)}} {\sqrt {(2x 4)(x-1)}} {\sqrt {(2x 2)(x-1)}}={\sqrt {(4x 2)(x 3)}}$

לכן

${\sqrt {(2x 4)(2x 2)}} {\sqrt {(2x 4)(x-1)}}={\sqrt {(4x 2)(x 3)}}-{\sqrt {(2x 2)(x-1)}}$

לכן

$(2x 4)(2x 2) (2x 4)(x-1) 2{\sqrt {(2x 4)^{2}(2x 2)(x-1)}}$ $=(4x 2)(x 3) (2x 2)(x-1)-2{\sqrt {(4x 2)(x 3)(2x 2)(x-1)}}$

לכן

$(6x^{2} 14x 4) 2{\sqrt {(2x 4)^{2}(2x 2)(x-1)}}=(6x^{2} 14x 4)-2{\sqrt {(4x 2)(x 3)(2x 2)(x-1)}}$

לכן

${\sqrt {(2x 4)^{2}(2x 2)(x-1)}}=-{\sqrt {(4x 2)(x 3)(2x 2)(x-1)}}$

כל ביטוי של שורש ריבועי מייצג מספר ממשי אי-שלילי, ומכאן שכל אחד מאגפי המשוואה הנ"ל חייב להיות מאופס, ולכן

$\textstyle 0=(2x 4)^{2}(2x 2)(x-1)=(4x 2)(x 3)(2x 2)(x-1)$

לכן

$x=\pm 1$

HOOTmag (talk) 22:04, 28 October 2009 (UTC)

That's interesting. I considered the fact that when you do a 2\3 split, you end up with 1\3 square roots and an additional pesky non-root term, which I thought to be as bad. I didn't think about the possibility that the plain terms from both sides would cancel.

Maybe something similar can happen with more terms. You do a 3\3 split where the plain term cancels, and then you still have 3\3, but with radicands of a different form which might lead to more cancellation. Meni Rosenfeld (talk) 05:59, 29 October 2009 (UTC)

No, six root-terms can't lead to more cancellation, I've checked this out (P.S. I see you've got an English keyboard only, right? well, never mind...) HOOTmag (talk) 09:19, 29 October 2009 (UTC)

No, it's just that in English I type faster, I can more easily express technical ideas, and the text aligns better.

להתחיל לכתוב פה בעברית נראה פשוט לא טבעי.-- Meni Rosenfeld (talk) 10:32, 29 October 2009 (UTC)

So, for what purpose did you indicate your Hebrew on your user page? I wouldn't do that on my user page if I didn't intend to ever use it... HOOTmag (talk) 10:59, 29 October 2009 (UTC)

I don't understand the question. The language userboxes are intended for providing information related to the language, not for actually conversing in the language. -- Meni Rosenfeld (talk) 12:25, 29 October 2009 (UTC)

I wouldn't think of that! "for providing information related to the language"! what a creative idea! So...I may need your help. Just today I was thinking about a question related to Hebrew. When referring to something very important, how should one say: "לא ניתן להפריז בחשיבותו", or - to the contrary: "לא ניתן להמעיט בחשיבותו". No Hebrew speaker is available here, so your opinion may be helpful. Thank you in advance. HOOTmag (talk) 16:25, 29 October 2009 (UTC)

Was that sarcasm? If so, I don't think I like where this discussion is going. Obviously what I meant was that the language userbox is directly relevant for people who do not themselves speak the language and do not live in a country where the language is spoken. See here and here for examples. -- Meni Rosenfeld (talk) 16:55, 29 October 2009 (UTC)

No sarcasm, I was definitely serious! your idea of presenting the language userbox on one's user page "for providing information related to the language", rather than for actually conversing in the language, is quite new to me: I'm used to a different behavior of wikipedians. Anyways, I took a look at the example - about the mathematical articles on Hebrew Wikipedia: I'm rather familiar with them (not with all of them, of course): a considerable part of them (mainly those in absract Algebra) is really of high quality, and has been written (especially for Wikipedia) by Professor Uzi Vishne, who is expert at his field and is also a very active wikipedian there. Furthermore, some of the Hebrew mathematical articles (mainly in advanced math) are even better and more detailed than the English ones (thanks to Prof. Vishne). However, you're correct: Hebrew Wikipedia doesn't have enough math articles (whose current quantity I estimate to be about 1,500), and some of them are relatively shorter than their English parallels. HOOTmag (talk) 19:33, 29 October 2009 (UTC)

Ok. It seemed odd to call "creative" what I believe is the well-understood intended usage. But I haven't really done any research on this, and I guess everyone uses it for the purposes he sees fit.

All that aside - as you may have noticed, I do not mind sharing personal information in my userpage, and I consider the languages I speak to be a very important detail. -- Meni Rosenfeld (talk) 20:11, 29 October 2009 (UTC)

Since you already asked - I think the former is correct, as long as it is understood to be a figure of speech - nothing is literally impossible to overvalue. -- Meni Rosenfeld (talk) 16:55, 29 October 2009 (UTC)

What still bothers me is the fact that the Hebrew speaker tends to use both phrases, as you can see here and here, for the same meaning, although they contradict each other, right? I was thinking about that - just today, and some hours later (when I read your clarification regarding the language userbox) I thought to myself that you might solve the riddle: How come the Hebrew speakers use contradictory phrases for the same meaning, and which phrase is "more correct", from a logical point of view. HOOTmag (talk) 19:33, 29 October 2009 (UTC)

I think the issue is with the meaning of ניתן. If it is used in the sense of "able" then the former is correct - something is important if you are unable to overvalue it. If it is used in the sense of "permitted" then the latter is correct - something is important if you should not undervalue it. Consistent with my previous observation, I believe "able" is the more correct sense. -- Meni Rosenfeld (talk) 20:11, 29 October 2009 (UTC)

Your analysis seems to be reasonable. Thank you. HOOTmag (talk) 21:26, 29 October 2009 (UTC)

Anyway, you should try the more sophisticated techniques recently suggested there. -- Meni Rosenfeld (talk) 05:59, 29 October 2009 (UTC)

Nomination for deletion of Template:Whitespace

Template:Whitespace has been nominated for deletion. You are invited to comment on the discussion at the template's entry on the Templates for discussion page. Thank you. Plastikspork _―Œ^(talk) 01:11, 4 January 2010 (UTC)

Thank you for your response

The concept "f is a bijection from A to B" has a very strict unambiguous definition. Whatever is a "bijection f from A to B" according to the classical definition, is also a "bijection f from A to B" according to the following definition:

• f is a correspondence (relation) on a given domain of discourse. A,B are included in that domain of discourse
• Every element, to which an element in A is corresponding (by f), is in B.
• For every s,t: if a given element is corresponding (by f) to s and to t, then s=t.
• For every s,t in A: if s,t are corresponding (by f) to a given element, then s=t.

What happens if I delete the words "in A" from the last condition? Then I get another definition, very similar (and almost equivalent) to the first one. Yet, the two alternative definitions are not equivalent to each other: For example, the correspondence (on the real numbers): "be the opposite number of" can be restricted to a bijection from the set of negative numbers to the set of positive numbers - according to both definitions, while the correspondence (on the real numbers) "be the square of" can be restricted to a bijection from the set of negative numbers to the set of positive numbers - according to the first definition only, yet not according to the second one - which doesn't enable the restriction.

Let's call the first definition (described above): "the extended definition of classical bijection", and let's call the last definition (received by deleting the words "in A"): "the definition of strong bijection". My question is about whether there is a simple brief term for what I call "strong bijection", or I have to explicitly display the second definition whenever I have to use "strong bijections".

HOOTmag (talk) 10:55, 15 March 2010 (UTC)

I think you've forgotten a key ingredient in the definition of bijection:

• f is a function.

A function is not a vague description of correspondence between objects, it is a concrete mathematical object, defined in one of several ways according to an author's taste. I like to use "a set of ordered pairs, in which the first item of any two pairs is distinct". The domain of a function is the set of elements that are a first item in a pair. Then it doesn't make any sense to talk about an s which is not in A corresponding to anything by f.

If you say "For every s" where s can be anything, it's not guaranteed that the correspondence you have in mind makes sense in such generality. What you can do is define $f(x)=x^{2}$ where x is in some large domain (which can include reals, complexes, square matrices, and other stuff) and talk about which restrictions of f are bijections. Not the other way around - you can't start with a small domain and assume that f can be extended to arbitrary domains.

As I said earlier, a concept which more closely matches what you want is a wff. Even then you need some notion of what your domain of discourse is, but it doesn't have to be a set. -- Meni Rosenfeld (talk) 11:27, 15 March 2010 (UTC)

Who talked about a function? I'm talking about what I call classical bijection and about what I call strong bijection. I gave a strict definition for either concept. The first definition (i.e. for the classical bijection) is an extended definition of a bijective function, while the second definition (i.e. for the strong bijection) is not intended to point at any function but rather at a correspondence (which is a strong bijection). My question is whether I need to explicitly display the second definition whenever I have to point at "strong bijections", or I can take a shorter way for pointing at them.

According to your suggestion, how should I say, simply, that there exists a strong bijection from A to B?

HOOTmag (talk) 12:34, 15 March 2010 (UTC)

I don't think your concept of "strong bijection" makes sense. If we try to make sense of it, I suspect we'll get that "there exists a strong bijection from A to B" holds precisely when there exists a bijective function from A to B, in other words, when $|A|=|B|$.

Anyway, I'm not an expert or anything, and I think you'll have better luck trying again at the refdesk. -- Meni Rosenfeld (talk) 12:52, 15 March 2010 (UTC)

As I exemplified above, the correspondence (on the real numbers): "be the opposite number of" can be restricted - both to a classical bijection and to a strong bijection - from the set of negative numbers to the set of positive numbers, while the correspondence (on the real numbers) "be the square of" can only be restricted to a classical bijection (not to a strong restriction) - from the set of negative numbers to the set of positive numbers. HOOTmag (talk) 13:04, 15 March 2010 (UTC)

Is it correct that "Be the square of" cannot be restricted to a strong bijection because "be the square of" is not a bijection of real numbers? If so, why not just say that "be the square of" is not a bijection of real numbers? Why do you insist on naming a property for the restriction, when it's clearly not a property of the restriction but of the correspondence you started with? There are correspondences which are bijections of the reals but whose restriction to negative numbers is the same as that of "be the square of". -- Meni Rosenfeld (talk) 13:22, 15 March 2010 (UTC)

What do you mean by: There are correspondences which are bijections of the reals but whose restriction to negative numbers is the same as that of "be the square of"? Can you give an example?

Anyways, you're right: if a function f is not a classical bijection, then also every "greater" function of which f can be a restriction - is not a classical bijection. Hence, "be the square of" is not a classical bijection from the negative numbers to the positive numbers, because it's not a classical bijection on the reals. However, note that the opposite is false: there are functions which are not classical bijections and still have restrictions which are classical bijections.

Anyways, my point is that there are correspondences which can be restricted to classical bijections (from A to B) yet not to strong bijections (from A to B). Therefore, claiming that f can be restricted to a "strong bijection from A to B" is much stronger than claiming that f can only be restricted to a "classical bijection from A to B". What I'm looking for is a brief elegant way of asserting the strong claim, namely of asserting that f is a "strong bijection from A to B", without using my new term "strong bijection", and without having to explicitly display the definition of strong bijection.

HOOTmag (talk) 13:55, 15 March 2010 (UTC)

Giving an example is harder because you want to use English rather than mathematical language, but think about $g(x)=-x|x|$. It is bijective on the reals and its restriction to negative numbers is the same as that of $g(x)=x^{2}$.

The second paragraph is very confusing - the first sentence is true, but the second is false and relies on the converse of the first.

I'll say again that the way to express "f can be restricted to a strong bijection from A to B" is "f is a bijection". -- Meni Rosenfeld (talk) 15:06, 15 March 2010 (UTC)

Don't you agree with my following statement?

• Claiming that f can be restricted to a "strong bijection from A to B" is much stronger than claiming that f can be restricted to a "classical bijection from A to B".

By a "stronger" claim I mean that the claim requires more than expected: not only does it require that f be able to be restricted to a "classical bijection from A to B", but it also requires that f be able to be restricted to a "strong bijection from A to B". Note that the relation "be the opposite number of" fulfills this strong requirement (when A is the set of negative numbers and B is the set of positive numbers), whereas the relation "be the square of" doesn't fulfill that requirement (A and B being defined as mentioned above), although both relations fulfill the weaker requirement, which refers to classical bijections only.

I don't agree with you that stating that "f is a bijection" - is equivalent to stating that "f can be restricted to a strong bijection from A to B". Here is a counter example: The identity bijection can't be restricted - neither to a classical bijection nor to a strong bijection - from the negative numbers to the positive numbers.

HOOTmag (talk) 15:32, 15 March 2010 (UTC)

I agree with 1st paragraph 15:32, but it doesn't address my objection to 2nd paragraph 13:55.

Re 2nd 15:32 - right, I thought that was a given but if you want to be more explicit - "f can be restricted to a strong bijection from A to B" iff "f is a bijection and can be restricted to a bijection from A to B". This assumes that the domain of f is the universal set to which "strong bijection" applies. -- Meni Rosenfeld (talk) 18:33, 15 March 2010 (UTC)

Re your first comment: I couldn't find the exact sentence to which you have an objection. Anyway, it doesn't matter as much, because now we are in a new phase, as you can see below...

Re your second comment: Excellent! your last equivalence is now helping me to be "more explicit" (as you've put it)...

Given that f is a correspondence (on a given universal domain of discourse), the idea of "f has a bijective restriction from A to B" - has a very strict unambiguous meaning, which is equivalent to the following definition:

1. A,B are sub-sets of F's universal domain of discourse.

2. For every s,t in B: if a given element in A is corresponding (by f) to s and to t, then s=t.

3. For every s,t in A: if s,t are corresponding (by f) to a given element in B, then s=t.

4. Every element, to which an element in A is corresponding (by f), is in B.

What happens if - due to considerations of symmetry (with the fourth condition) - I add the following condition?

5. Every element, which is corresponding (by f) to an element in B, is in A.

Then I get another definition, very similar to the first one. Yet, the two alternative definitions are not equivalent to each other: For example, the correspondence (on the real numbers): "be the opposite number of" has a bijective restriction from the set of negative numbers to the set of positive numbers - according to both definitions, while the correspondence (on the real numbers) "be the square of" has a bijective restriction from the set of negative numbers to the set of positive numbers - according to the first definition only, yet not according to the second one - which doesn't enable the bijective restriction.

Let's call the first definition (described above): "the definition of classical bijective restriction", and let's call the second definition (received by adding the fifth condition): "the definition of strong bijective restriction". My question is about whether there is a simple brief expression for what I call "strong bijective restriction", or I have to explicitly display the second definition whenever I have to use "strong bijective restrictions".

Note that for getting such a simple brief expression, I can't use your equivalence: "f has a strong bijective restriction from A to B" iff "f is a bijection and has a bijective restriction from A to B". Here is a counter example: a function which maps every positive number to itself and also maps every non-positive number to zero. It's not a bijection, yet it has a strong bijective restriction - from the set of positive numbers to itself.

HOOTmag (talk) 20:50, 15 March 2010 (UTC)

Ok, now I understand what you're asking. No, I don't know any concise term for this. However, condition 5 can be stated in terms of preimage as $f^{-1}(B)\subseteq A$. This notation is usually used for functions, but it should be understood for general correspondences.

To have a bijective restriction from A to B you also need the conditions "every element of A corresponds to some item by f" and "for every element of B, some item corresponds to it".

By the way, did you read Binary relation? -- Meni Rosenfeld (talk) 08:50, 16 March 2010 (UTC)

Yes I did, mainly the chapter about restriction.

According to your suggestion, to state that "the binary relation f has a strong bijective restriction from A to B" - is equivalent to stating that "the binary relation f has a (classical) bijective restriction from A to B, and $f^{-1}(B)\subseteq A$".

Do I have also to add that $f(A)\subseteq B$? Here is a case for consideration: f is a correspondence (on the complex plane) by which every number corresponds to its two square roots; Note that f has neither classical bijective restrictions - nor strong bijective restrictions - from the set A of positive numbers to the set B of negative numbers...

Notice that - for the notion of "bijective restriction" - I'm looking for an elegant brief expression, namely, it should both be symmetric and include no redundant speech. Why "symmetric"? Because the very notion of "bijection" involves a symmetry between the bijection and its inverse bijection.

HOOTmag (talk) 09:46, 16 March 2010 (UTC)

$f(A)\subseteq B$, which is condition 4, is not necessary in order to be able to restrict f to a bijection from A to B. But it is necessary if you want that just restricting the domain of f to A will make it a bijection to B. -- Meni Rosenfeld (talk) 10:24, 16 March 2010 (UTC)

Note that my question about adding the condition $f(A)\subseteq B$, referred to your suggested equivalent for the notion of strong bijective restriction, so I'm not sure I really understood well your answer, so let's put it as explicitly as possible, by my following two explicit questions:

1. If f is a correspondence (on the complex plane) by which every number corresponds to its two square roots, then do you think that f has any classical bijective restriction from the set A of positive numbers to the set B of negative numbers?

2. If I want to indicate that f has a strong bijective restriction from A to B, but I don't want to use the very term of "strong bijective restriction", then: do I have to state that "f has a (classical) bijective restriction from A to B, and $f(A)\subseteq B$, and $f^{-1}(B)\subseteq A$", or can I avoid stating that "$f(A)\subseteq B$"?

HOOTmag (talk) 11:43, 16 March 2010 (UTC)

1. Yes, the relation $\{(a,b)|a>0,b<0,b^{2}=a\}$ is a restriction of f which is a bijection from A to B.
2. Yes, the condition $f(A)\subseteq B$ appears in your definition of "strong bijective restriction" and does not follow from the existence of a classical bijective restriction, so you have to include it.

-- Meni Rosenfeld (talk) 12:04, 16 March 2010 (UTC)

Thank you for your clear response. So according to your suggestion, If I want to indicate that the correspondence f has a strong bijective restriction from A to B, but I don't want to use the very term of "strong bijective restriction", then I have to state that "f has a bijective restriction from A to B, and $f(A)\subseteq B$, and $f^{-1}(B)\subseteq A$". Clumsy a bit, but that's what we've got...

What happens if I replace the correspondence by a formula? Let me explain my question:

If $\varphi$ is a formula having two free variables only (over the universal domain of discourse), then: to state that $\varphi$ induces a bijection from R to S, means that:

• Every r in R has an s in S such that for every v in S : $\varphi (r,v)$ iff v=s.
• Every s in S has an r in R such that for every u in R : $\varphi (u,s)$ iff u=r.

That's a simple definition of a bijection induced by a given formula.

But what happens if we let u,v be totally arbitrary, i.e. let them belong to the universal domain of discourse, unnecessarily to a given set?

Then we can say that $\varphi$ strongly-induces a bijection from R to S, namely:

• Every r in R has an s in S such that for every v : $\varphi (r,v)$ iff v=s.
• Every s in S has an r in R such that for every u : $\varphi (u,s)$ iff u=r.

Can you think of any idea about how to express briefly the fact that $\varphi$ strongly-induces a bijection from R to S, without using the term "strongly", and without having to get into too many details (like those I've indicated above when I defined the notion of "strongly-inducing a bijection")?

HOOTmag (talk) 14:16, 16 March 2010 (UTC)

Unfortunately, no, I cannot. -- Meni Rosenfeld (talk) 10:14, 17 March 2010 (UTC)

What a pity...

Anyways, thank you for your help up to now. I appreciate it.

All the best, take care, good luck.

HOOTmag (talk) 11:34, 17 March 2010 (UTC)

Hello

I've just put it at the Reference desk. Have a nice day. HOOTmag (talk) 08:33, 18 March 2010 (UTC)

You too, good luck. -- Meni Rosenfeld (talk) 08:38, 18 March 2010 (UTC)

Prove

Hello. You suggested the identities of $a\cdot (b\times c)=b\cdot (c\times a)$ and $(a\times b)\times (a\times c)=(a\cdot (b\times c))a$ to prove (${\overrightarrow {u}}$ × ${\overrightarrow {v}}$) ⋅ ((${\overrightarrow {v}}$ × ${\overrightarrow {w}}$) × (${\overrightarrow {w}}$ × ${\overrightarrow {u}}$)) = (${\overrightarrow {u}}$ ⋅ (${\overrightarrow {v}}$ × ${\overrightarrow {w}}$))². My left side looks like: (${\overrightarrow {u}}$ × ${\overrightarrow {v}}$) ⋅ (${\overrightarrow {u}}$ ⋅ (${\overrightarrow {v}}$ × ${\overrightarrow {w}}$))${\overrightarrow {w}}$. How should I proceed? Thanks in advance. --Mayfare (talk) 22:17, 4 June 2010 (UTC)

Note that the ${\overrightarrow {u}}\cdot ({\overrightarrow {v}}\times {\overrightarrow {w}})$ you have in the middle is just a scalar you can take out of the whole thing. What you're left with is something you can easily manipulate into what you need.

PS. Look at how I've typeset these formulas - the way you've done it is more complicated than necessary. -- Meni Rosenfeld (talk) 18:01, 5 June 2010 (UTC)

Thanks

for your help here. —Preceding unsigned comment added by 130.88.243.41 (talk) 09:08, 11 June 2010 (UTC)

No problem. -- Meni Rosenfeld (talk) 09:13, 11 June 2010 (UTC)

Subset Question

Meni, I hope you don't mind me approaching you on your talk page. I always though that the natural numbers were contained in the integers, which were themselves contained in the rational numbers, which were themselves contained in the real numbers, which were themselves contained in the complex numbers, which were themselves contained in the quaternions, i.e. ℕ ⊂ ℤ ⊂ ℚ ⊂ ℝ ⊂ ℂ ⊂ ℍ.

A question on the mathematics reference desk seems to have replies which claim, for example, that the integers are not a subset of the real numbers. This seems to be something to do with the formal definition of the integers and/or the real numbers. But how can this be? Is there a definition of the real numbers that says that −1 is not a real number? That 0 is not a real number? That 1 is not a real number?

Surely we have: If n is an integer then n is a real number? Therefore ℤ ⊂ ℝ. •• Fly by Night (talk) 14:07, 19 June 2010 (UTC)

I don't at all mind being asked here, but to avoid confusion, it's better to continue the discussion at the reference desk. -- Meni Rosenfeld (talk) 19:00, 19 June 2010 (UTC)

Thanks!

Many thanks for the help on the question I had on correlation coefficient. You helped me a lot :-) - 114.76.235.170 (talk) 14:06, 12 August 2010 (UTC)

You're welcome :) . -- Meni Rosenfeld (talk) 15:44, 12 August 2010 (UTC)

Sorry for the thousands of questions... still trying to work out why you need to get the product of the z-scores to get the correlation coefficient. But I'll ask a bit later on the RD! - 114.76.235.170 (talk) 02:24, 13 August 2010 (UTC)

AIV

If you're looking at an active infestation, take it to WP:Administrator intervention against vandalism. If Materialscientist is offline, he won't be able to do anything to help you, and if you're talking about the same individual who's plaguing Materialscientist's talk page, you don't need to inform him (and you're only feeding the attention-seeker there). — JohnFromPinckney (talk) 09:21, 22 August 2010 (UTC)

Stop dobbing

Stop dobbing on me mate. We can be mates if ya wanna. Stop dobbing and get a life. —Preceding unsigned comment added by 110.20.58.220 (talk) 10:31, 22 August 2010 (UTC)

See the history of your user page mate and carefuly see what's written in the revision

Hiya! —Preceding unsigned comment added by 120.22.76.208 (talk) 12:43, 28 September 2010 (UTC)

Reverted. The Thing // Talk // Contribs 12:46, 28 September 2010 (UTC)

And Revision Deleted and page protected indefinitely. Courcelles 13:11, 28 September 2010 (UTC)

Great, thanks. -- Meni Rosenfeld (talk) 13:26, 28 September 2010 (UTC)

Beaten again

Rumplestilskin (talk) 20:57, 8 October 2010 (UTC)This makes about the fourth time I have tried to contribute something to Wikipedia, or even to ask a question. It is also the fourth time I have gotten absolutely nowhere. Wikipedia is a mystery to me. I just don't understand it, and I don't think I'll even try again. Life is too short, and I don't want to shorten the time that I have left my spending hours of frustrating, irritating, and unproductive time to unravel its mysteries. I will continue to use Wikipedia, but I have to give up on trying to interact with it.

Here's what I was trying to do this time. I was trying to comment on something I saw at the following address: <http://en.wikipedia.org/wiki/My_Buddy_(song)>

Rumplestilskin (talk) 20:57, 8 October 2010 (UTC)This article states the following: It is universally believed this song was written about a World War soldier who lost his friend in battle. Well, you'll have to change this to "almost universally," because Charles Marowitz believes differently. In his article "The Neglected Walter Donaldson," Mr. Marowitz says the following: " His most durable song may well have been My Buddy written in l922, inspired by the unexpected and heartbreaking death of his young fiancé and curiously adopted during World War II as a song about male camaraderie among the allied troops. A simple but mesmerizing waltz tune, which, sung by an evocative singer, can still subdue a noisy nightclub audience into a reverent silence".

Wikipedia is too tough for me to use, but I have nothing but admiration for it. Keep up the good work.

Comments like this should be posted on the article's talk page (which is done the same way that you've added this post to my talk page). I have done this for you, you may want to check back there for replies. -- Meni Rosenfeld (talk) 16:30, 9 October 2010 (UTC)

Goldbach Partition

Hi Meni, Your interesting comment, "I've done some numerical investigation and it looks like the correct expression is ${\frac {n}{2\ln ^{2}n-4\ln n-c}}$, where c tends to some number around 0.7 (maybe it's $\ln 2$)" really got my attention. After thinking it over for a few days, I am still baffled. Would it be possible for you to shed some light on how you derived the expression?

Concerning my issue regarding "(without regard to order)," I feel that my question about exactly what the Goldbach partition counting function is enumerating is still kind of up in the air. In my opinion, mathworld's article, Goldbach Partition seems to adequately address this issue, but then muddies the water with an extra function $R(2n)$. This issue is centered upon exactly what it is that we actually mean when we call something a Partition (or a Composition for that matter). This got me to thinking that as Wikipedeans, we are in a good position to do a much better job (than say, mathworld) of resolving this seemingly mundane issue. While I was mulling this over, I found an interesting short paper, On Partitions of Goldbach’s Conjecture by Max See Chin Woon that contains the seeds of a slightly more formal definition for Goldbach Partitions. To explain myself in better detail, I would be happy to prepare a short paper (prototype wiki article, 'Goldbach Partition') for you, if you are interested. What do you think? Best regards, Mathup (talk) 05:35, 17 February 2011 (UTC)

P.S.: As an aside (and this could be nothing), I propose candidate for the constant in the vicinity of $\ln 2$; could it possibly be the Twin prime constant? Mathup (talk) 05:35, 17 February 2011 (UTC)

Basically what I did is use Mathematica to calculate ${\frac {n}{\sum _{m=3}^{n/2}{\frac {1}{\log m\log(n-m)}}}}$ for various values of n, and fit a quadratic function of $\log n$ to the results. I tried it over several ranges and the coefficients of $\ln ^{2}n,\ \ln n$ always came very close to 2 and -4, respectively, so it's safe to assume these are the true values. Finding the constant term is harder, but I've done a more accurate calculation now and it seems to be around 0.7101 - so it's neither ln2 nor the twin prime constant. If I was able to find it with greater accuracy I would look it up in Plouffe's inverter.

My impression from the Mathworld article is that there's no standard as to which way to count the number of partitions. It's just one of those things that if it matters to what you're doing, you have to explicitly state how you're defining it.

Anyway, PrimeHunter, who has also replied to your question, is more knowledgeable about everything related to primes (he picked this username for a reason), and you may want to talk with him as well. But I suspect the best place for a clarification about partition counting would be within the Goldbach's conjecture article, in which case the best place to discuss it is the article'ss talk page. -- Meni Rosenfeld (talk) 09:43, 17 February 2011 (UTC)

Thanks, Meni. Your spot on analysis is just what I needed. It will take me a while to digest what you've done. Before we move this thread to the the article'ss talk page, I want to be sure that I understand your position. Is my position unsupportable because there does not appear to be any conventional or standard terminology 'out there' (mathworld, et. al.)? Do you agree that the operative words here are 'standard' and 'conventional'? Please don't get me wrong, since it's clear to me that mathworld is an extremely valuable resource that complements what we are doing here and vise versa. In my opinion, Mathworld's 'micro-article', Goldbach Partition almost hits the nail on the head, but stops short when they introduce the second Goldbach counting function $R(2n)$ without giving us any clue as to the 'conventional' number-theoretic name for it (the 'Goldbach composition counting function' as opposed to the 'Goldbach partition counting function', $r(2n)$ and inside an article about partitions? ). Is it un-encyclopedic for us to assume a leadership role and nail down some absent at best or loose at worst (IMHO) conventional/customary/standard terminology? I think that our apparent divergence does not come to the fore until we attempt to actually count those Goldbach puppies. I think convention can step in to save the day, for example, mathworld's article Partition states, "By convention[<--operative word alert], partitions are normally written from largest to smallest addends (Skiena 1990, p. 51)." My issue is that this conventional usage should[<--operative word alert] apply to Goldbach partitions and Goldbach compositions as well. I have been unable to find any meaningful literature about Goldbach compositions -- it's all Goldbach partitions this and Goldbach partitions that. Goldbach schmartitions! Maybe two new sections to Goldbach's conjecture will be in order (or reverse order)[<--sarcasm alert]. Maybe this apparently unnecessary naming rigor upon which I have been harping could cause a small paradigm shift that carries us a little closer to a better understanding Goldbach's Conjecture. Or, maybe not. We will never know if we don't try it out.

I hope that I have not tried your patience too much. I know that you have bigger fish to fry at the institute and I want to thank you for corresponding with me and shining your expert math luminescence on my benign (at first glance) questions and concerns. I hope that you will still be available when subsequent related questions slowly ooze into my faded math consciousness. In local street parlance, "Meni, you da man!"--Mathup (talk) 18:37, 17 February 2011 (UTC)

Yes, it seems to me that there are two ways of counting Goldbach partitions, which Mathworld calls $r(2n)$ and $R(2n)$ (I don't know if that notation is standard, either!) and no conventional names for distinguishing them. If this is the case then it is wrong to attempt to establish a standard on Wikipedia - I think the relevant Wikipedia policy is WP:OR, even though this is not "research" per se.

However, I could be wrong and in fact there is a convention which is known to people involved in this field but difficult to find online. To find out Talk:Goldbach's conjecture is the best place. I'll remind you that I find the issue fairly insignificant - I don't really believe there is any great insight to be obtained by clarifying it.

I'm afraid I only have a very limited ability to answer your questions about Goldbach's conjecture and related issues. But other issues that have been raised, like evaluating sums and numerical exploration of functions, are things I'm more enthusiastic about and will be happy to answer more questions. -- Meni Rosenfeld (talk) 20:16, 17 February 2011 (UTC)

Hi Meni, Yes, $r(2n)$ and $R(2n)$ are not standard notation as far as I can tell. After some drilling down, I found the same notation in only one paper Fractal in the statistics of Goldbach partition. In a cursory survey of the literature, I found the most common notation for the Goldbach partition counting function to be $g(2n)$ and sometimes $g_{p}(2n)$. Both seem quite reasonable to me, but are nonstandard nonetheless. However, my point that $R(2n)$ counts compositions and does not count partitions is probably forever lost. Since number theorists, like cowboys are a rare breed and Goldbach is a relatively obscure sub-specialty horse in the number theory stable, I wouldn't expect standardized notation for the Goldbach partition counting function. However, the clear and concise math definitions for the English words 'partition' and 'composition' are routinely misused, even by smart people who 'ought' know better, thereby substituting choas for progress on the Goldbach front, in my humble opinion. I guess I'm willing to live with it if they are. You have pointed me in the right direction to help me understand why Wikipedia may not be the proper venue to create an small enclave of order inside a the whirlwind of chaos. I realize that I'm dancing on the edge of what might be construed by some as 'original research' and am now more inclined to just let the sleeping doggies lie, since there is not a plethora of sources to reference. I suspect that your assessment that the issue is fairly insignificant may be well founded. But, wouldn't it delightful if we are both wrong? I admire your willingness to tread into strange waters outside your specialty. Finding myself in the unenviable position of being my own research director, I'll definitely let you know if I happen upon something less insignificant. I'll have some more questions about evaluating summations with ugly summands as I trundle into the future. Until then, shalom Mathup (talk) 23:09, 17 February 2011 (UTC)

RFA (Request for Approximation)

Hi Meni, Hope all is well with you. After groping in the dark all night, I've made a modicum of progress. Would it be possible for you to numerically investigate the following summation for me?

$f(2n)=\sum _{i=1}^{n-2}{\frac {(2i 1)(2n-2i-1)}{\log(2i 1)\log(2n-2i-1)}}$.

My best naive guess for the highest order term so far is

$f(2n)\approx {\frac {n^{3}}{3\log ^{2}2n}}$.

Take care, Mathup (talk) 16:26, 18 February 2011 (UTC)

I got

$f(2n)\approx {\frac {n^{3}}{1.5\log ^{2}n-b\log n-c}}$

where $b\approx 0.420558458$ and is probably $2.5-3\log 2$, and $c\approx 0.6281$.

By the way, you probably know that $\log ^{2}2n=(\log n \log 2)^{2}=\log ^{2}n 2\log 2\log n \log ^{2}2\;\!$, so any quadratic in $\log 2n$ can be expressed as a quadratic in $\log n$. I prefer the latter form.

As an exercise, you can use a calculator or a programming language to find the sum for some sufficiently large value of n, and compare it to the two approximations. -- Meni Rosenfeld (talk) 17:13, 19 February 2011 (UTC)

Hi Meni, This useful (to me) result looks really good at first glance. With conflicting priorities, I won't be able to test it thoroughly straight away, but I'll get back to you as time permits. Thank you soo...o much, Meni! Shalom, Mathup (talk) 00:45, 20 February 2011 (UTC)

My triplet prime question on maths ref desk

Thanks Meni (rather belated) for your clear and concise answer to my question as to whether triplet primes are possible. Of course, now I see that they cannot exist, but I did immediately note that in the case of twin primes, the even number separating them MUST always be divisible by three. What an insight, eh?

And I was very interested to hear that there is no formal proof that the set of twin primes is infinite! Myles325a (talk) 08:21, 5 March 2011 (UTC)

You're welcome. -- Meni Rosenfeld (talk) 17:08, 5 March 2011 (UTC)

Angle of rotation of an ellipse

Hello,

I saw your post about the angle of rotation of an ellipse, I'd never seen it done that way before - it's very neat.

I'd normally use a more heavy-handed approach of taking a standard ellipse ${\frac {x^{2}}{a^{2}}} {\frac {y^{2}}{b^{2}}}=1$, rotating to an arbitrary angle $y=y^{\prime }cos(\theta ) x^{\prime }sin(\theta )$ etc., substituting in and expanding and then comparing coefficients. Your version is much less work - thanks! —Preceding unsigned comment added by Christopherlumb (talk • contribs) 18:26, 21 May 2011 (UTC)

No problem. Transforming the coordinate system is indeed the more general-purpose approach, but for this case we can make use of the specific properties of ellipses. I don't think I saw this method before either, I made it up on the spot. -- Meni Rosenfeld (talk) 08:43, 22 May 2011 (UTC)

Life agars

Belated thanks for your reply on Wikipedia:Reference desk/Archives/Mathematics/2011 May 17#Life density. I got way behind on my watchlist. —Tamfang (talk) 07:58, 15 June 2011 (UTC)

You're welcome. -- Meni Rosenfeld (talk) 08:15, 15 June 2011 (UTC)

Oblivious algorithm

The RD entry is getting huge, so I thought I'd place this here. You made me dig all the way to the 1920's for this one, but you've helped me in the past so I don't mind... This request is not popular, so it isn't worked on much in computer science. It was semi-popular as an attempted variation of the Dining Philosophers problem. The following solution is a compilation of notes I pulled from various old papers and books:

Everyone has the same algorithm:

1. Get the initial text.
2. If all entries are marked as "DONE", just read the messages and pass the completed text along. Note: You'll eventually get it back again - don't forward a completed text twice.
3. Locate your entry in the text.
4. If your entry is complete, mark it as DONE.
5. Otherwise, randomly choose to remove something from your text, add garbage to your text, or add part of your real message to your text.
6. Randomly shuffle the lines of text.
7. Pass it on to the next user

In your 3-person example, let's assume they are trying to make 3 numbers. A chooses the number 6. B chooses the number 42. C chooses the number 123:

1. A adds 4 to the text (garbage) and sends it to B.
2. B adds 2 at the bottom so the text now has 4 on one line and 2 on another. B knows A added 4. No need to shuffle - it won't make a difference here.
3. C adds 2 at the top of the text. He shuffles so the top 2 lines have a 2 and the bottom line has a 4. C doesn't know who added 4 and who added 2.
4. A identified 4 on the last line and places a 0 after it to make the line 40. The lines are shuffled so it is 40, then 2, then 2. A knows both B and C entered a 2.
5. B sees the file. He suspects A entered 40. He identifies either entry of 2 as his. He places a 4 in front of it. The file is shuffled so it has 42 then 2 then 40.
6. C still has no idea who entered 40 or 42. He adds 3 after his 2 and shuffles it sending 40 42 23 to A.
7. A changes her line containing 40 to 6. She sends 42 6 23 to B.
8. B is now confused. He knows 42 is his line. He can guess that 23 might belong to C, but C could have replaced the 2 with a 6 while A replaced 40 with 23. Anyway, he marks his line as done sending 42DONE 23 6 to C.
9. C adds a 1 before 23 and sends 6 123 42DONE to A.
10. A marks hers as done sending 123 42DONE 6DONE to B.
11. B notices his is done, but there's still work. So, he sends 6DONE 123 42DONE to C.
12. C marks his as done. One more pass around and everyone knows the numbers 6, 42, and 123.

This works with any number of participants, but it has been criticized as non-terminating. Theoretically, adding a maximum number of rounds makes it possible to force a user to give information that may identify his/her entry. However, smart encoding of the protocol will have "garbage" lines purposely mimic what is in the file, obscuring the user's entries. I hope this is usable for you. -- kainaw™ 14:49, 20 September 2011 (UTC)

This is interesting, but doesn't look specific enough. How do the people know what actions to take to sufficiently obfuscate their message? Thanks. -- Meni Rosenfeld (talk) 15:05, 20 September 2011 (UTC)

My opinion, based on attacks of the various attempts at this algorithm, is that the only problem is that the first transfer is the only transfer of who entered what. B knows what A put on the list. C never has a chance to know anything. Therefore, it is only necessary for A to confuse B. That can be done. Here's a scenario going in A B C order:

1. 12
2. 12 4
3. 6 12 4
4. 24 6 4

Now, B doesn't know if 24 or 6 came from A or C. When C gets the next round, the 24 will look eerily similar to the previous 4 (and we don't know what B will change the 4 to). So, C doesn't know which is A or which is C. The trick is for A's second edit to be something that is similar to what is already entered. It truly becomes a task of predicting the next value in a random number generator. It is possible, but not practical - and nowhere near as practical as matching up plain text to cipher text once the protocol and key lengths are known. -- kainaw™ 15:56, 20 September 2011 (UTC)

I find Kainaw's approach interesting... but it does seem to have some disadvantages like terminating, and I wonder if there are data analysis ways to judge who's changing what. Collusion is still an issue too.

Schneier describes an algorithm by Chum that's sort of similar to this, but more formalized: 3 participants, A, B, C want top send a message to everyone but they don't want the recipients to know who sent it. A round consists of:

1. each pair (AB AC CB) flip a coin together
2. each participant declares if the two flips they observed are the same or different; however, if a participant wants to send a [set] bit they invert their answer

Because if no participant inverts their answer there will always be an even number of "different" responses, the participants can deduce someone is sending a 1 bit if the number of "different" responses are odd. However it's impossible to know who (collusion is a problem, but as you scale n participants the amount of collusion required increases). You'd also need checksums to catch multiple senders and a random backoff so that only one person's sending a message for x number of rounds, but all of those problems are fixable in a given protocol.

I'm actually considering writing an implementation of this. The papers related to it are: D. Chum, "The dining cryptographers problem: unconditional sender aand receiver untraceability", Journal of Cryptography, v1 n1 1988. p 65-75; tamper evident version: B. Pfitzmann and M. Waidner, "Unconditional Concealment with Cryptographic Ruggedness", VIS '91 Verlassliche Inforrmationsysteme Proceedings, Darmstadt, Germany, 13-15 March 1991, p 3-2-320; M. Waidner and B. Pftizmann, "The Dining Cryptographers int he Disco: Unconditional Sender and Recipient Untraceability with Computationally Secure Serviceability," Advances in Cryptology-CRYPTO '86 Proceedings, Sringer-Verlag, 1987, p393-404. Shadowjams (talk) 20:07, 24 September 2011 (UTC)

I didn't find any real-world implementations the algorithm I described. I don't see why it needs to be so complicated. Why can't it be this simple:

When you first see the message list go by, add a secret word to it that only you know about and scramble the list.

When you see the message list the second time, replace your secret word with your message and scramble the list.

When you see the message list the third time, it has everyone's message on it.

The only limitation is that the secret words and the messages must be similar in length and pattern. So, nobody can tell if an entry in the message list is a secret word or a message. -- kainaw™ 18:12, 25 September 2011 (UTC)

Because you transmit your message in full all at once. It's trivial to know who sent it. In your step 1 B knows what A sent and C knows what either A or B sent. I just provided a simple solution that'd demonstrably proven by professional cryptographers with 3 citations. Shadowjams (talk) 21:30, 25 September 2011 (UTC)

Yes, you transmit your message in full all at once. But, how is it trivial to know who sent it? Consider that you are B. You get "43" from A. You send "43/8" to C. You wait and you get "94/109/8" back. Who put 94 in the message? Who put 109 in the message? -- kainaw™ 14:35, 26 September 2011 (UTC)

After re-reading old papers on this, it is necessary to have unknown termination. Once termination is known (in two rounds in the example I just gave), knowledge of who posted what is revealed. -- kainaw™ 13:30, 27 September 2011 (UTC)

The system leaks information at each step. I'm confused as Meni is because I don't see explicit rules, just an example. What I'm gathering is that at each step, participants either add garbage or real data, or alternatively subtract garbage data. The problem is you'll always know what changes were made in each round and you can begin to categorize that information. Even worse if participants collude or you see multiple steps in the chain (in the Chum algorithm traffic analysis is unhelpful).

Out of curiosity, are there papers or proofs that gave you the idea for this? Maybe I'm missing the underlying principle, but the example alone isn't helping me get it.

The system I describe is hardly complicated. It uses only two basic principles: bitwise inversion and remote coinflipping. Remote coin-flipping can easily be done with a basic commitment scheme XOR. The biggest downside to it is that it's open to active, anonymous denial of service. However with a checksum added that would be detectable [even if the culprit were unknown]. As the other references provide too, there are tamper resistant versions of the same protocol that are more complicated. Shadowjams (talk) 23:01, 27 September 2011 (UTC)

Angle trisection

Please reconsider the proof mentioned in the reference desk.The angle is indeed trisected.--117.227.118.221 (talk) 16:15, 30 October 2011 (UTC)Baibhab Pattnaik

No, it is not. As Dmcq suggests, try this with a 120 degree angle and you'll see that it's divided to 30,60,30 degrees. -- Meni Rosenfeld (talk) 17:05, 30 October 2011 (UTC)

Can you please check if the angles formed by joining the vertex angle to the points of trisection of the base trisect the vertex angle?--117.226.210.176 (talk) 12:02, 31 October 2011 (UTC)Baibhab Pattnaik

I checked, they do not trisect the angle. If angle AOB is $\alpha$ then the angle POQ is $2\tan ^{-1}\left({\frac {1}{3}}\tan {\frac {\alpha }{2}}\right)$ rather than ${\frac {\alpha }{3}}$. Please also read Angle trisection. -- Meni Rosenfeld (talk) 20:09, 31 October 2011 (UTC)

Intuitive summation.

Hi, thanks for the nice answer at Wikipedia:Reference_desk/Mathematics#Summation_beginner!! Such intuition-building approaches is what's missing from maths as it is usually presented! Thanks, -- WillNess (talk) 09:02, 16 December 2011 (UTC)

No problem, glad to be of help. I agree, it is too common to find some simple elegant point being obscured by an overly dry and mechanical presentation. -- Meni Rosenfeld (talk) 13:49, 16 December 2011 (UTC)

Thank you!

(barnstar by NorwegianBlue moved)

You're welcome, and thanks! I've placed the barnstar on my userpage. -- Meni Rosenfeld (talk) 14:06, 12 April 2012 (UTC)

"Fire bet"

I'm putting this here because of multiple edit conflicts. Feel free to copy it to the ref desk. The fire bet is only available on the shooter's first come out roll. The numbers "2", "3", "7", "11", and "12" are irrevelant for the fire bet, so we'll disregard those. The shooter rolls until s/he throws a "4", "5", "6", "8", "9", or "10". Let's say the shooter rolls a "6". This number is the "point". The shooter continues to roll until a "7" is thrown and s/he loses, or a "6" is thrown, in which case the point is made and one-sixth of the fire bet is complete. The shooter must continue in this fashion, establishing a point, and making each point without rolling a "7" first. Any "7" thrown on a come out roll does not affect the fire bet. If the shooter establishes, and makes a "6", and then establishes and makes another "6", the second "6" is irrevelant to the fire bet. "4", "5", "6", "8", "9", and "10" must each be established (thrown on the come out roll), then made (thrown after the come out roll, before a "7" is thrown). Any "7" thrown between the establishing and making of a point renders the bet lost. Please let me know if I need to clarify anything else. Joefromrandb (talk) 20:08, 26 April 2012 (UTC)

American Jews

Hello Meni Rosenfeld, I am working on American Jews article now and I would like to ask you to translate the phrase "American Jews" or "Jewish Americans" into Hebrew. Is there a common name for Jews living in the US in Hebrew language? If yes, please let me know.--Yerevanci (talk) 18:51, 9 August 2012 (UTC)

Hi Yerevanci, I don't know of any special term for that, I would just use the literal translation "יהודים אמריקאים". -- Meni Rosenfeld (talk) 20:38, 9 August 2012 (UTC)

Thanks very much. And do you know Yiddish? I know it's a Germanic language and has little to do with Hebrew, but if you do, please write its translation, too.--Yerevanci (talk) 21:27, 9 August 2012 (UTC)

I don't know Yiddish, sorry. -- Meni Rosenfeld (talk) 21:08, 11 August 2012 (UTC)

Statistical induction and prediction

Hello Meni! We have had interesting discussions regarding statistical induction and prediction. You may like to read my article www.academia.edu/3247833 . The result is not reported in wikipedia because it is original research. Your comments and corrections are welcome. Yours truly, Bo Jacoby (talk) 21:27, 1 February 2014 (UTC).

Hi Bo, thanks for the offer. Unfortunately I don't currently have the time to examine your paper. -- Meni Rosenfeld (talk) 23:31, 1 February 2014 (UTC)

Charging for Doing Homework

The most difficult and time-consuming part of my response to the homework question was checking that I could source the "special bonus" wine glasses sufficiently cheaply to still make a profit on the total package! As it happens, I'm planning to use what I wrote in my answer to the question about simultaneous linear equations in a rather more interesting way than the question might suggest... One of the courses I have to teach this year includes a section on information asymmetry, and as I was writing my original, rather shorter, response to the homework question it occurred to me that I could use this case as a nice introductory example. The prospective customer doesn't know who I am, nor does he have any idea of my abilities, so how can I persuade him to use my services? Of course I can offer a lower price, but I also need a way of signalling that I am capable of providing him with correct information. In my offer I therefore use various strategies. First, I show that I am more competent than my competitor by finding a failure in my competitor's offering that is obvious to the prospective buyer (I count the number of questions correctly) and provide a correction for free (there are four questions). Second, I find an obvious failure in my competitor's offering (he hasn't spotted the typo in 1.3) and indicate that I can provide the correct solution to the pair of equations in that question, but instead of doing so I provide information about my answer that the prospective buyer can check without my providing the answer immediately. Third, I provide general, publicly available evidence of my competence that the buyer can check immediately (my large number of edits to Wikipedia). Fourth, I provide (or in this case offer to provide) specific testimonials from previous people who have been able to assess my expertise (my degree certificates). Fifth, I signal my confidence in my ability to deliver the correct solutions by incurring a (potential) cost (I agree to a costly penalty) if my answers are wrong. Sixth, I signal that I am confident that on average my business model is profitable and that he will use my services again by agreeing to provide an introductory discount or bonus (in this case a non-cash bonus in the form of wine glasses or cuddly toy). Though not all of these are perfect examples of their kind, nor have I exhaustively covered all the possible things I could do to address the information asymmetry between myself and the prospective buyer who doesn't know how well I can provide my services, I have created an example that can be used in the course I shall be teaching. Even the time I spent on this response to you is time well-spent, as it has helped me get my thoughts and wording clear in my mind! RomanSpa (talk) 16:30, 4 February 2015 (UTC)

Your last statement was reassuring, because at 1.3 BTC/hour, I certainly had no intention to pay for the time it took you to write this response! :) -- Meni Rosenfeld (talk) 17:00, 4 February 2015 (UTC)

moving sofa problem

I made an edit to define lower bound and upper bound in that article, but someone keeps reverting it and accusing me of being wrong. here. You seem to have a good knowledge about math. Maybe you can tell them that I'm not wrong, or you can explain to me what's wrong with my definition if it's indeed wrong. Thanks! — Preceding unsigned comment added by 146.151.84.226 (talk) 17:12, 24 February 2015 (UTC)

Thank you for contacting me. Unfortunately, I believe you are in fact wrong, as I tried to explain at some length in the reference desk. Honestly, I'm not sure what I can say to make it clearer, but I'll try.

You say "the upper bound is the smallest area that cannot go through it." This is false - there is no smallest area that cannot go through (except 0). For every $A\geq 0$, however small, there is a shape of area A that cannot go through.

You also say "A lower bound is the largest area that can go through the hallway". Also incorrect - the largest area that can go through is simply called "the sofa constant". We do not know what the sofa constant is, because nobody solved the moving sofa problem yet. All we know about the sofa constant is that it is between 2.219531669... and 2.8284... . Therefore, we say that 2.219531669 is a lower bound on the sofa constant, and 2.8284... is an upper bound. -- Meni Rosenfeld (talk) 17:59, 24 February 2015 (UTC)

Well, after I read your answer in the reference desk, I think I understand the problem completely now. Ok I see what you mean now. I was wrong because I didn't phrase the wordings correctly, but I knew what it is. I meant to say that the lower bound is the largest area that can go through the hallway that we currently know. For upper bound, while I understand entirely what it means now, it's hard to express in words concisely. Let's me try again, the upper bound is the smallest area we know that, for all possible shapes of sofa, cannot go through. I believe it's essential to include the meanings for lower bound and upper bound for this specific problem in this article. That's not something we can safely assume most readers can understand. I'm trying to improve Wikipedia here. Can you add in the acceptable definitions for them? I have been marked up now. If I add it in, it's likely my edit would be reverted again. Thanks!146.151.90.74 (talk) 20:52, 24 February 2015 (UTC)

I think it's sufficiently clear as it is. The lede defines what the sofa constant is; the next section then gives the known lower and upper bounds on the constant. Lower and upper bounds are general terms; and the way they apply to this particular problem is completely given by the fact that we are talking about the previously defined sofa constant.

Most readers who would understand the article at all would understand this, and be able to fill in any gaps using common sense. In fact, making it too verbose could actually make it less clear.

Perhaps there should be a link to Upper and lower bounds, so people unfamiliar with the terms can refer to that. But this article doesn't currently have much information on this use case for bounds; perhaps it's worth it to work on that article and explain it a bit more. -- Meni Rosenfeld (talk) 21:44, 24 February 2015 (UTC)

Well, we can think of it the other way around. Clear explanations on the lower and upper bound will help the readers understand the article more. The Upper and lower bounds wouldn't help much, since its definitions are too abstract. It's unlikely anyone would understand unless one is a math major. I understand what upper bound and lower bound were, but I did not understand it clearly until I read your comment in the reference desk. I think by making it more clear it would only make it better.146.151.90.74 (talk) 22:21, 24 February 2015 (UTC)

You should bring it up for discussion at Talk:Moving_sofa_problem. -- Meni Rosenfeld (talk) 22:45, 24 February 2015 (UTC)

I'm not a Wikipedia editor and not interested to be one. I don't feel like getting involved too much with it. I was told everyone can edit including me but apparently not. The edits must satisfy the opinions of some established editors. My words literally weigh nothing compared to them. In a debate, I would likely to lose. I came to Wikipedia to read about the sofa problem and felt some more information is needed so I added in to make Wikipedia better. This is why Wikipedia does not get more editors. The environment is not friendly to new comers. Wikipedia editors are discouraging non-editors like me to edit even though I saw a big banner saying that everyone can edit. Since I can't add in the information myself that I think would improve the article (makes it more accessible to more people; I'm sure as its current standing, it would be too hard for most readers to understand anyway), I was just asking you to help adding it in. Not trying to criticize you. I'm just saying, if you don't want to do it then it's fine. I don't want to argue with other editors that clearly oppose its inclusion. Okay, thanks for your explanation again. I don't think there is any reason for me to be involved with Wikipedia anymore. I'll be gone. Peace!146.151.90.74 (talk) 23:25, 24 February 2015 (UTC)

You are a Wikipedia editor, by definition - you have edited an article on Wikipedia. This is regardless of the facts that you have not yet created an account, and that you haven't done many edits.

Your edits were removed not because of some status wars, but simply because other editors (myself included!) don't think your edits, however well-meaning, improved Wikipedia. Wikipedia is a collaborative encyclopedia, and this means it is crucial to be able to respect the opinions of others, discuss them hoping to reach agreement, and occasionally having to face the fact that others may disagree with you. No editor has the right to have their edits intact if the consensus is against them.

Again, status has little bearing on this. Many new editors write edits that remain intact, and many veteran editors have their edits reverted and need to convince the other editors of the validity of their edits. here is a recent example for an edit of mine which was reverted (in this case I opted to accept the judgement of the other editor rather than arguing my point). And I can assure you that if I were to put in the same edit you did, it would be reverted very quickly.

Blaming others for this disagreement, as you've done here, is the easy cop-out. Accepting personal responsibility (in this case, for your opinion which is rejected by others) is harder. So is working to find how you can still contribute to Wikipedia, such as:

• Discussing on the article talk page, as I have suggested, trying to explain why you think your edit should stay. Perhaps, with the help of other editors, you can find some sort of compromise which addresses everyone's concerns.
• Letting the matter drop, and finding other articles that need improvement. Making many different edits and having some of them stick, will be more effective than obsessing about a single edit.

Wikipedia needs more editors, and I hope the above encourages you to continue to try to find your way in it. But if not, that's also fine. I'll say again - Wikipedia is collaborative, you don't own your edits, and everyone has as much right to revert your edits as you have have the right to make them. Editing Wikipedia is right for you only if you can accept this simple fact. -- Meni Rosenfeld (talk) 17:26, 25 February 2015 (UTC)

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Probability of lucky streak in Poisson process

[3] Hi Meni. Did your problem get a satisfactory solution? Happy new year! Bo Jacoby (talk) 11:18, 5 January 2016 (UTC).

Hi Bo, thanks for following up. I didn't yet have a chance to examine your latest suggestions. I'll let you know if I manage to make something work.

Thanks. -- Meni Rosenfeld (talk) 12:52, 5 January 2016 (UTC)

Reference desk

I wanted to thank you for your thoughtful, patient posts here. Because this is the internet (and because of the behavior of the interlocutor), I am not exactly optimistic about them having a good effect, but they are much better than anything I would have written. Thanks! --JBL (talk) 12:32, 28 April 2016 (UTC)

Hi Joel, thanks for your message! Proper civility in discussions is something I care about, so I thought I would share my thoughts on the matter.

For reference, while I agree an apology by the OP was in order, I personally view the instance as below the threshold where an apology should be demanded if not given voluntarily.

As for the effectiveness of this... The same OP has a few days ago shown another sign of lack of proper respect to the people on the RefDesk, so it might just be who he is and there's no getting to him. I tend to believe the OP is essentially well-meaning but hasn't developed a feel for the finer points of discussion etiquette. In my experience this is a topic for which it's difficult to convince about the proper ways, one either has it or he doesn't. I remember this discussion on Quora where, like here, I tried to illuminate someone else's criticism of an OP, and the more I tried to explain my position, the more some people just wrote me off as a troll... -- Meni Rosenfeld (talk) 14:38, 28 April 2016 (UTC)

I agree that this was below the normal threshold for "requires comment"; if anything, I would say that the previous episode you mention played a role in my choosing to complain. (Possibly, this reflects poorly on my own choices.) The Quora thread is interesting (and the first comment is very much correct: a terrible question that inspired a great answer, though maybe the question-asker cannot appreciate it); at least it didn't get so heated in the end.

It is too bad that there is not a culture at the reference desk of requiring better behavior from question-askers, or at least from regulars. Best wishes, JBL (talk) 16:24, 28 April 2016 (UTC)

Cubic function

I know I asked this question many times before in the mathematics page, but I'd like to ask you personally:
Is it possible to unlock $x$ out of the cubic $ax^{3} bx^{2} cx d=0$ - without at all changing variables as $x=y-{\frac {a}{3}}$ to reduce the equation to a suppressed cubic our even quadratic?

You see, what I'm trying to avoid is using variables "out of nowhere" without understanding how. As you know, in the quadratic $ax^{2} bx c=0$ it's pretty trivial. How many times could I ask this - is it at all possible to avoid anomalies like this!? יהודה שמחה ולדמן (talk) 00:44, 21 June 2016 (UTC)

Are you talking about expressing the solution, or finding it in the first place?

If the former, then Cubic_function#Algebraic_solution provides an expression for the solution that does not explicitly introduce a new variable.

If the latter, I'm not sure why you are looking for that. The substitution clearly works and gives us an easier equation to work with. Why are you opposed to making things easier?

In any case, I don't really know about alternative ways to derive the solution to the general cubic equation. -- Meni Rosenfeld (talk) 01:33, 21 June 2016 (UTC)

Why am I opposed to making things easier? Well, as I said, in the quadtatic there is no such thing as variable changing, all you need to realize is why completing the square is wise.

So, I want to find out if anyone can do the same in cubics, because here I keep seeing a different method of using $x=y-{\frac {a}{3}}$ with no proof how we got it at first without guessing. I don't like guessing.

And yes, we read about higher degrees of $n\geq 5$ which according to math have no solving algorithms, in which you need to use other ways like Bisection method including guesses. יהודה שמחה ולדמן (talk) 10:46, 21 June 2016 (UTC)

But it's obvious that if you substitute $x=y-{\frac {b}{3a}}$ (not $x=y-{\frac {a}{3}}$ as you wrote) you get rid of the quadratic term. It follows from the binomial expansion $(a b)^{3}=a^{3} 3a^{2}b O(a)$ .

Even if you don't consider it obvious - why is that a problem? There is no mechanical algorithm that takes a statement and finds a proof for it. If there was, the life of mathematicians would be much easier. But instead they need to use their creativity to find proofs to theorems. And really, any step taken in any proof can be considered "guessing", since you don't know if it will help you until you try it out. -- Meni Rosenfeld (talk) 21:23, 21 June 2016 (UTC)

What is $O(b^{2})$ ? And how does $x=y-{\frac {b}{3a}}$ follow from this? יהודה שמחה ולדמן (talk) 21:47, 21 June 2016 (UTC)

See Big O notation. Note also that what I actually meant to write was $O(a)$.

You want $x=y-\alpha$ such that the expansion of $ax^{3}=a(y-\alpha )^{3}$ has a term $-by^{2}$ which will cancel out the $by^{2}$. From the expansion above you have $a(y-\alpha )^{3}=ay^{3}-3ay^{2}\alpha O(y)$. So you want $-3ay^{2}\alpha by^{2}=0$, meaning that $\alpha ={\frac {b}{3a}}$. -- Meni Rosenfeld (talk) 21:53, 21 June 2016 (UTC)

MfD nomination of Wikipedia:Help desk/RD tip 1 (plain)

Wikipedia:Help desk/RD tip 1 (plain), a page which you created or substantially contributed to, has been nominated for deletion. Your opinions on the matter are welcome; you may participate in the discussion by adding your comments at Wikipedia:Miscellany for deletion/Wikipedia:Help desk/RD tip 1 (plain) and please be sure to sign your comments with four tildes (~~~~). You are free to edit the content of Wikipedia:Help desk/RD tip 1 (plain) during the discussion but should not remove the miscellany for deletion template from the top of the page; such a removal will not end the deletion discussion. Thank you. Pppery (talk) 02:44, 6 August 2016 (UTC)

Thanks for the notice. I've made a comment there but overall, I haven't used these templates in years, so I'll trust the judgement of those who are actively using them. -- Meni Rosenfeld (talk) 17:51, 6 August 2016 (UTC)

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Wishing Meni Rosenfeld a very happy birthday on behalf of the Birthday Committee!   interstatefive  (talk) - just another roadgeek 00:01, 16 May 2022 (UTC)

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