SRC/cggsvd3.f

*> \brief <b> CGGSVD3 computes the singular value decomposition (SVD) for OTHER matrices</b>
*
*  =========== DOCUMENTATION ===========
*
* Online html documentation available at
*            http://www.netlib.org/lapack/explore-html/
*
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*> \endhtmlonly
*
*  Definition:
*  ===========
*
*       SUBROUTINE CGGSVD3( JOBU, JOBV, JOBQ, M, N, P, K, L, A, LDA, B,
*                           LDB, ALPHA, BETA, U, LDU, V, LDV, Q, LDQ, WORK,
*                           LWORK, RWORK, IWORK, INFO )
*
*       .. Scalar Arguments ..
*       CHARACTER          JOBQ, JOBU, JOBV
*       INTEGER            INFO, K, L, LDA, LDB, LDQ, LDU, LDV, M, N, P, LWORK
*       ..
*       .. Array Arguments ..
*       INTEGER            IWORK( * )
*       REAL               ALPHA( * ), BETA( * ), RWORK( * )
*       COMPLEX            A( LDA, * ), B( LDB, * ), Q( LDQ, * ),
*      $                   U( LDU, * ), V( LDV, * ), WORK( * )
*       ..
*
*
*> \par Purpose:
*  =============
*>
*> \verbatim
*>
*> CGGSVD3 computes the generalized singular value decomposition (GSVD)
*> of an M-by-N complex matrix A and P-by-N complex matrix B:
*>
*>       U**H*A*Q = D1*( 0 R ),    V**H*B*Q = D2*( 0 R )
*>
*> where U, V and Q are unitary matrices.
*> Let K L = the effective numerical rank of the
*> matrix (A**H,B**H)**H, then R is a (K L)-by-(K L) nonsingular upper
*> triangular matrix, D1 and D2 are M-by-(K L) and P-by-(K L) "diagonal"
*> matrices and of the following structures, respectively:
*>
*> If M-K-L >= 0,
*>
*>                     K  L
*>        D1 =     K ( I  0 )
*>                 L ( 0  C )
*>             M-K-L ( 0  0 )
*>
*>                   K  L
*>        D2 =   L ( 0  S )
*>             P-L ( 0  0 )
*>
*>                 N-K-L  K    L
*>   ( 0 R ) = K (  0   R11  R12 )
*>             L (  0    0   R22 )
*>
*> where
*>
*>   C = diag( ALPHA(K 1), ... , ALPHA(K L) ),
*>   S = diag( BETA(K 1),  ... , BETA(K L) ),
*>   C**2   S**2 = I.
*>
*>   R is stored in A(1:K L,N-K-L 1:N) on exit.
*>
*> If M-K-L < 0,
*>
*>                   K M-K K L-M
*>        D1 =   K ( I  0    0   )
*>             M-K ( 0  C    0   )
*>
*>                     K M-K K L-M
*>        D2 =   M-K ( 0  S    0  )
*>             K L-M ( 0  0    I  )
*>               P-L ( 0  0    0  )
*>
*>                    N-K-L  K   M-K  K L-M
*>   ( 0 R ) =     K ( 0    R11  R12  R13  )
*>               M-K ( 0     0   R22  R23  )
*>             K L-M ( 0     0    0   R33  )
*>
*> where
*>
*>   C = diag( ALPHA(K 1), ... , ALPHA(M) ),
*>   S = diag( BETA(K 1),  ... , BETA(M) ),
*>   C**2   S**2 = I.
*>
*>   (R11 R12 R13 ) is stored in A(1:M, N-K-L 1:N), and R33 is stored
*>   ( 0  R22 R23 )
*>   in B(M-K 1:L,N M-K-L 1:N) on exit.
*>
*> The routine computes C, S, R, and optionally the unitary
*> transformation matrices U, V and Q.
*>
*> In particular, if B is an N-by-N nonsingular matrix, then the GSVD of
*> A and B implicitly gives the SVD of A*inv(B):
*>                      A*inv(B) = U*(D1*inv(D2))*V**H.
*> If ( A**H,B**H)**H has orthonormal columns, then the GSVD of A and B is also
*> equal to the CS decomposition of A and B. Furthermore, the GSVD can
*> be used to derive the solution of the eigenvalue problem:
*>                      A**H*A x = lambda* B**H*B x.
*> In some literature, the GSVD of A and B is presented in the form
*>                  U**H*A*X = ( 0 D1 ),   V**H*B*X = ( 0 D2 )
*> where U and V are orthogonal and X is nonsingular, and D1 and D2 are
*> ``diagonal''.  The former GSVD form can be converted to the latter
*> form by taking the nonsingular matrix X as
*>
*>                       X = Q*(  I   0    )
*>                             (  0 inv(R) )
*> \endverbatim
*
*  Arguments:
*  ==========
*
*> \param[in] JOBU
*> \verbatim
*>          JOBU is CHARACTER*1
*>          = 'U':  Unitary matrix U is computed;
*>          = 'N':  U is not computed.
*> \endverbatim
*>
*> \param[in] JOBV
*> \verbatim
*>          JOBV is CHARACTER*1
*>          = 'V':  Unitary matrix V is computed;
*>          = 'N':  V is not computed.
*> \endverbatim
*>
*> \param[in] JOBQ
*> \verbatim
*>          JOBQ is CHARACTER*1
*>          = 'Q':  Unitary matrix Q is computed;
*>          = 'N':  Q is not computed.
*> \endverbatim
*>
*> \param[in] M
*> \verbatim
*>          M is INTEGER
*>          The number of rows of the matrix A.  M >= 0.
*> \endverbatim
*>
*> \param[in] N
*> \verbatim
*>          N is INTEGER
*>          The number of columns of the matrices A and B.  N >= 0.
*> \endverbatim
*>
*> \param[in] P
*> \verbatim
*>          P is INTEGER
*>          The number of rows of the matrix B.  P >= 0.
*> \endverbatim
*>
*> \param[out] K
*> \verbatim
*>          K is INTEGER
*> \endverbatim
*>
*> \param[out] L
*> \verbatim
*>          L is INTEGER
*>
*>          On exit, K and L specify the dimension of the subblocks
*>          described in Purpose.
*>          K   L = effective numerical rank of (A**H,B**H)**H.
*> \endverbatim
*>
*> \param[in,out] A
*> \verbatim
*>          A is COMPLEX array, dimension (LDA,N)
*>          On entry, the M-by-N matrix A.
*>          On exit, A contains the triangular matrix R, or part of R.
*>          See Purpose for details.
*> \endverbatim
*>
*> \param[in] LDA
*> \verbatim
*>          LDA is INTEGER
*>          The leading dimension of the array A. LDA >= max(1,M).
*> \endverbatim
*>
*> \param[in,out] B
*> \verbatim
*>          B is COMPLEX array, dimension (LDB,N)
*>          On entry, the P-by-N matrix B.
*>          On exit, B contains part of the triangular matrix R if
*>          M-K-L < 0.  See Purpose for details.
*> \endverbatim
*>
*> \param[in] LDB
*> \verbatim
*>          LDB is INTEGER
*>          The leading dimension of the array B. LDB >= max(1,P).
*> \endverbatim
*>
*> \param[out] ALPHA
*> \verbatim
*>          ALPHA is REAL array, dimension (N)
*> \endverbatim
*>
*> \param[out] BETA
*> \verbatim
*>          BETA is REAL array, dimension (N)
*>
*>          On exit, ALPHA and BETA contain the generalized singular
*>          value pairs of A and B;
*>            ALPHA(1:K) = 1,
*>            BETA(1:K)  = 0,
*>          and if M-K-L >= 0,
*>            ALPHA(K 1:K L) = C,
*>            BETA(K 1:K L)  = S,
*>          or if M-K-L < 0,
*>            ALPHA(K 1:M)=C, ALPHA(M 1:K L)=0
*>            BETA(K 1:M) =S, BETA(M 1:K L) =1
*>          and
*>            ALPHA(K L 1:N) = 0
*>            BETA(K L 1:N)  = 0
*> \endverbatim
*>
*> \param[out] U
*> \verbatim
*>          U is COMPLEX array, dimension (LDU,M)
*>          If JOBU = 'U', U contains the M-by-M unitary matrix U.
*>          If JOBU = 'N', U is not referenced.
*> \endverbatim
*>
*> \param[in] LDU
*> \verbatim
*>          LDU is INTEGER
*>          The leading dimension of the array U. LDU >= max(1,M) if
*>          JOBU = 'U'; LDU >= 1 otherwise.
*> \endverbatim
*>
*> \param[out] V
*> \verbatim
*>          V is COMPLEX array, dimension (LDV,P)
*>          If JOBV = 'V', V contains the P-by-P unitary matrix V.
*>          If JOBV = 'N', V is not referenced.
*> \endverbatim
*>
*> \param[in] LDV
*> \verbatim
*>          LDV is INTEGER
*>          The leading dimension of the array V. LDV >= max(1,P) if
*>          JOBV = 'V'; LDV >= 1 otherwise.
*> \endverbatim
*>
*> \param[out] Q
*> \verbatim
*>          Q is COMPLEX array, dimension (LDQ,N)
*>          If JOBQ = 'Q', Q contains the N-by-N unitary matrix Q.
*>          If JOBQ = 'N', Q is not referenced.
*> \endverbatim
*>
*> \param[in] LDQ
*> \verbatim
*>          LDQ is INTEGER
*>          The leading dimension of the array Q. LDQ >= max(1,N) if
*>          JOBQ = 'Q'; LDQ >= 1 otherwise.
*> \endverbatim
*>
*> \param[out] WORK
*> \verbatim
*>          WORK is COMPLEX array, dimension (MAX(1,LWORK))
*>          On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
*> \endverbatim
*>
*> \param[in] LWORK
*> \verbatim
*>          LWORK is INTEGER
*>          The dimension of the array WORK.
*>
*>          If LWORK = -1, then a workspace query is assumed; the routine
*>          only calculates the optimal size of the WORK array, returns
*>          this value as the first entry of the WORK array, and no error
*>          message related to LWORK is issued by XERBLA.
*> \endverbatim
*>
*> \param[out] RWORK
*> \verbatim
*>          RWORK is REAL array, dimension (2*N)
*> \endverbatim
*>
*> \param[out] IWORK
*> \verbatim
*>          IWORK is INTEGER array, dimension (N)
*>          On exit, IWORK stores the sorting information. More
*>          precisely, the following loop will sort ALPHA
*>             for I = K 1, min(M,K L)
*>                 swap ALPHA(I) and ALPHA(IWORK(I))
*>             endfor
*>          such that ALPHA(1) >= ALPHA(2) >= ... >= ALPHA(N).
*> \endverbatim
*>
*> \param[out] INFO
*> \verbatim
*>          INFO is INTEGER
*>          = 0:  successful exit.
*>          < 0:  if INFO = -i, the i-th argument had an illegal value.
*>          > 0:  if INFO = 1, the Jacobi-type procedure failed to
*>                converge.  For further details, see subroutine CTGSJA.
*> \endverbatim
*
*> \par Internal Parameters:
*  =========================
*>
*> \verbatim
*>  TOLA    REAL
*>  TOLB    REAL
*>          TOLA and TOLB are the thresholds to determine the effective
*>          rank of (A**H,B**H)**H. Generally, they are set to
*>                   TOLA = MAX(M,N)*norm(A)*MACHEPS,
*>                   TOLB = MAX(P,N)*norm(B)*MACHEPS.
*>          The size of TOLA and TOLB may affect the size of backward
*>          errors of the decomposition.
*> \endverbatim
*
*  Authors:
*  ========
*
*> \author Univ. of Tennessee
*> \author Univ. of California Berkeley
*> \author Univ. of Colorado Denver
*> \author NAG Ltd.
*
*> \ingroup complexGEsing
*
*> \par Contributors:
*  ==================
*>
*>     Ming Gu and Huan Ren, Computer Science Division, University of
*>     California at Berkeley, USA
*>
*
*> \par Further Details:
*  =====================
*>
*>  CGGSVD3 replaces the deprecated subroutine CGGSVD.
*>
*  =====================================================================
      SUBROUTINE CGGSVD3( JOBU, JOBV, JOBQ, M, N, P, K, L, A, LDA, B,
     $                    LDB, ALPHA, BETA, U, LDU, V, LDV, Q, LDQ,
     $                    WORK, LWORK, RWORK, IWORK, INFO )
*
*  -- LAPACK driver routine --
*  -- LAPACK is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*
*     .. Scalar Arguments ..
      CHARACTER          JOBQ, JOBU, JOBV
      INTEGER            INFO, K, L, LDA, LDB, LDQ, LDU, LDV, M, N, P,
     $                   LWORK
*     ..
*     .. Array Arguments ..
      INTEGER            IWORK( * )
      REAL               ALPHA( * ), BETA( * ), RWORK( * )
      COMPLEX            A( LDA, * ), B( LDB, * ), Q( LDQ, * ),
     $                   U( LDU, * ), V( LDV, * ), WORK( * )
*     ..
*
*  =====================================================================
*
*     .. Local Scalars ..
      LOGICAL            WANTQ, WANTU, WANTV, LQUERY
      INTEGER            I, IBND, ISUB, J, NCYCLE, LWKOPT
      REAL               ANORM, BNORM, SMAX, TEMP, TOLA, TOLB, ULP, UNFL
*     ..
*     .. External Functions ..
      LOGICAL            LSAME
      REAL               CLANGE, SLAMCH
      EXTERNAL           LSAME, CLANGE, SLAMCH
*     ..
*     .. External Subroutines ..
      EXTERNAL           CGGSVP3, CTGSJA, SCOPY, XERBLA
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC          MAX, MIN
*     ..
*     .. Executable Statements ..
*
*     Decode and test the input parameters
*
      WANTU = LSAME( JOBU, 'U' )
      WANTV = LSAME( JOBV, 'V' )
      WANTQ = LSAME( JOBQ, 'Q' )
      LQUERY = ( LWORK.EQ.-1 )
      LWKOPT = 1
*
*     Test the input arguments
*
      INFO = 0
      IF( .NOT.( WANTU .OR. LSAME( JOBU, 'N' ) ) ) THEN
         INFO = -1
      ELSE IF( .NOT.( WANTV .OR. LSAME( JOBV, 'N' ) ) ) THEN
         INFO = -2
      ELSE IF( .NOT.( WANTQ .OR. LSAME( JOBQ, 'N' ) ) ) THEN
         INFO = -3
      ELSE IF( M.LT.0 ) THEN
         INFO = -4
      ELSE IF( N.LT.0 ) THEN
         INFO = -5
      ELSE IF( P.LT.0 ) THEN
         INFO = -6
      ELSE IF( LDA.LT.MAX( 1, M ) ) THEN
         INFO = -10
      ELSE IF( LDB.LT.MAX( 1, P ) ) THEN
         INFO = -12
      ELSE IF( LDU.LT.1 .OR. ( WANTU .AND. LDU.LT.M ) ) THEN
         INFO = -16
      ELSE IF( LDV.LT.1 .OR. ( WANTV .AND. LDV.LT.P ) ) THEN
         INFO = -18
      ELSE IF( LDQ.LT.1 .OR. ( WANTQ .AND. LDQ.LT.N ) ) THEN
         INFO = -20
      ELSE IF( LWORK.LT.1 .AND. .NOT.LQUERY ) THEN
         INFO = -24
      END IF
*
*     Compute workspace
*
      IF( INFO.EQ.0 ) THEN
         CALL CGGSVP3( JOBU, JOBV, JOBQ, M, P, N, A, LDA, B, LDB, TOLA,
     $                 TOLB, K, L, U, LDU, V, LDV, Q, LDQ, IWORK, RWORK,
     $                 WORK, WORK, -1, INFO )
         LWKOPT = N   INT( WORK( 1 ) )
         LWKOPT = MAX( 2*N, LWKOPT )
         LWKOPT = MAX( 1, LWKOPT )
         WORK( 1 ) = CMPLX( LWKOPT )
      END IF
*
      IF( INFO.NE.0 ) THEN
         CALL XERBLA( 'CGGSVD3', -INFO )
         RETURN
      END IF
      IF( LQUERY ) THEN
         RETURN
      ENDIF
*
*     Compute the Frobenius norm of matrices A and B
*
      ANORM = CLANGE( '1', M, N, A, LDA, RWORK )
      BNORM = CLANGE( '1', P, N, B, LDB, RWORK )
*
*     Get machine precision and set up threshold for determining
*     the effective numerical rank of the matrices A and B.
*
      ULP = SLAMCH( 'Precision' )
      UNFL = SLAMCH( 'Safe Minimum' )
      TOLA = MAX( M, N )*MAX( ANORM, UNFL )*ULP
      TOLB = MAX( P, N )*MAX( BNORM, UNFL )*ULP
*
      CALL CGGSVP3( JOBU, JOBV, JOBQ, M, P, N, A, LDA, B, LDB, TOLA,
     $              TOLB, K, L, U, LDU, V, LDV, Q, LDQ, IWORK, RWORK,
     $              WORK, WORK( N 1 ), LWORK-N, INFO )
*
*     Compute the GSVD of two upper "triangular" matrices
*
      CALL CTGSJA( JOBU, JOBV, JOBQ, M, P, N, K, L, A, LDA, B, LDB,
     $             TOLA, TOLB, ALPHA, BETA, U, LDU, V, LDV, Q, LDQ,
     $             WORK, NCYCLE, INFO )
*
*     Sort the singular values and store the pivot indices in IWORK
*     Copy ALPHA to RWORK, then sort ALPHA in RWORK
*
      CALL SCOPY( N, ALPHA, 1, RWORK, 1 )
      IBND = MIN( L, M-K )
      DO 20 I = 1, IBND
*
*        Scan for largest ALPHA(K I)
*
         ISUB = I
         SMAX = RWORK( K I )
         DO 10 J = I   1, IBND
            TEMP = RWORK( K J )
            IF( TEMP.GT.SMAX ) THEN
               ISUB = J
               SMAX = TEMP
            END IF
   10    CONTINUE
         IF( ISUB.NE.I ) THEN
            RWORK( K ISUB ) = RWORK( K I )
            RWORK( K I ) = SMAX
            IWORK( K I ) = K   ISUB
         ELSE
            IWORK( K I ) = K   I
         END IF
   20 CONTINUE
*
      WORK( 1 ) = CMPLX( LWKOPT )
      RETURN
*
*     End of CGGSVD3
*
      END