#!/usr/bin/python
# -*- coding: utf8 -*-

import matplotlib.pyplot as plt
import matplotlib as mpl
import numpy as np
from math import *

code_website = 'http://commons.wikimedia.org/wiki/User:Geek3/mplwp'
try:
    import mplwp
except ImportError, er:
    print 'ImportError:', er
    print 'You need to download mplwp.py from', code_website
    exit(1)

name = 'mplwp_butterworth-filter-gain.svg'
fig = mplwp.fig_standard(mpl)
mplwp.set_bordersize(fig, 42.5, 42.5, 24.5, 26.5)

xlim = 0,3; fig.gca().set_xlim(xlim)
ylim = 0,1.1; fig.gca().set_ylim(ylim)
mplwp.mark_axeszero(fig.gca(), x0=1.0, y0=1.0)

import scipy.signal as sig
frange = np.linspace(0, 3.0, 3001)

for N in range(1, 4 1):
    (num, den) = sig.butter(N, 1.0, analog=True)
    filterfy = sig.freqs(num, den, frange)
    plt.title('Butterworth filter')
    plt.plot(filterfy[0], np.abs(filterfy[1]), lw=2,
             label='order {0}'.format(N), zorder=-N)

plt.xlabel('f/f$_0$')
plt.gca().xaxis.set_label_coords(1.05, 0.05)
plt.ylabel('G', rotation=0)
plt.gca().yaxis.set_label_coords(-0.03, 0.99)
plt.legend(loc='upper right')

plt.savefig(name)
mplwp.postprocess(name)