SRC/cgesvd.f(3)

NAME
SRC/cgesvd.f

SYNOPSIS

  Functions/Subroutines
subroutine cgesvd (jobu, jobvt, m, n, a, lda, s, u, ldu, vt, ldvt, work, lwork, rwork, info)
CGESVD computes the singular value decomposition (SVD) for GE matrices

Function/Subroutine Documentation

  subroutine cgesvd (character jobu, character jobvt, integer m, integer n, complex, dimension( lda, * ) a, integer lda, real, dimension( * ) s, complex, dimension( ldu, * ) u, integer ldu, complex, dimension( ldvt, * ) vt, integer ldvt, complex, dimension( * ) work, integer lwork, real, dimension( * ) rwork, integer info)

CGESVD computes the singular value decomposition (SVD) for GE matrices

Purpose:

     CGESVD computes the singular value decomposition (SVD) of a complex
     M-by-N matrix A, optionally computing the left and/or right singular
     vectors. The SVD is written
          A = U * SIGMA * conjugate-transpose(V)
     where SIGMA is an M-by-N matrix which is zero except for its
     min(m,n) diagonal elements, U is an M-by-M unitary matrix, and
     V is an N-by-N unitary matrix.  The diagonal elements of SIGMA
     are the singular values of A; they are real and non-negative, and
     are returned in descending order.  The first min(m,n) columns of
     U and V are the left and right singular vectors of A.
     Note that the routine returns V**H, not V.

Parameters
    JOBU

              JOBU is CHARACTER*1
              Specifies options for computing all or part of the matrix U:
              = 'A':  all M columns of U are returned in array U:
              = 'S':  the first min(m,n) columns of U (the left singular
                      vectors) are returned in the array U;
              = 'O':  the first min(m,n) columns of U (the left singular
                      vectors) are overwritten on the array A;
              = 'N':  no columns of U (no left singular vectors) are
                      computed.

    JOBVT

              JOBVT is CHARACTER*1
              Specifies options for computing all or part of the matrix
              V**H:
              = 'A':  all N rows of V**H are returned in the array VT;
              = 'S':  the first min(m,n) rows of V**H (the right singular
                      vectors) are returned in the array VT;
              = 'O':  the first min(m,n) rows of V**H (the right singular
                      vectors) are overwritten on the array A;
              = 'N':  no rows of V**H (no right singular vectors) are
                      computed.
              JOBVT and JOBU cannot both be 'O'.

    M

              M is INTEGER
              The number of rows of the input matrix A.  M >= 0.

    N

              N is INTEGER
              The number of columns of the input matrix A.  N >= 0.

    A

              A is COMPLEX array, dimension (LDA,N)
              On entry, the M-by-N matrix A.
              On exit,
              if JOBU = 'O',  A is overwritten with the first min(m,n)
                              columns of U (the left singular vectors,
                              stored columnwise);
              if JOBVT = 'O', A is overwritten with the first min(m,n)
                              rows of V**H (the right singular vectors,
                              stored rowwise);
              if JOBU .ne. 'O' and JOBVT .ne. 'O', the contents of A
                              are destroyed.

    LDA

              LDA is INTEGER
              The leading dimension of the array A.  LDA >= max(1,M).

    S

              S is REAL array, dimension (min(M,N))
              The singular values of A, sorted so that S(i) >= S(i+1).

    U

              U is COMPLEX array, dimension (LDU,UCOL)
              (LDU,M) if JOBU = 'A' or (LDU,min(M,N)) if JOBU = 'S'.
              If JOBU = 'A', U contains the M-by-M unitary matrix U;
              if JOBU = 'S', U contains the first min(m,n) columns of U
              (the left singular vectors, stored columnwise);
              if JOBU = 'N' or 'O', U is not referenced.

    LDU

              LDU is INTEGER
              The leading dimension of the array U.  LDU >= 1; if
              JOBU = 'S' or 'A', LDU >= M.

    VT

              VT is COMPLEX array, dimension (LDVT,N)
              If JOBVT = 'A', VT contains the N-by-N unitary matrix
              V**H;
              if JOBVT = 'S', VT contains the first min(m,n) rows of
              V**H (the right singular vectors, stored rowwise);
              if JOBVT = 'N' or 'O', VT is not referenced.

    LDVT

              LDVT is INTEGER
              The leading dimension of the array VT.  LDVT >= 1; if
              JOBVT = 'A', LDVT >= N; if JOBVT = 'S', LDVT >= min(M,N).

    WORK

              WORK is COMPLEX array, dimension (MAX(1,LWORK))
              On exit, if INFO = 0, WORK(1) returns the optimal LWORK.

    LWORK

              LWORK is INTEGER
              The dimension of the array WORK.
              LWORK >=  MAX(1,2*MIN(M,N)+MAX(M,N)).
              For good performance, LWORK should generally be larger.
              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.

    RWORK

              RWORK is REAL array, dimension (5*min(M,N))
              On exit, if INFO > 0, RWORK(1:MIN(M,N)-1) contains the
              unconverged superdiagonal elements of an upper bidiagonal
              matrix B whose diagonal is in S (not necessarily sorted).
              B satisfies A = U * B * VT, so it has the same singular
              values as A, and singular vectors related by U and VT.

    INFO

              INFO is INTEGER
              = 0:  successful exit.
              < 0:  if INFO = -i, the i-th argument had an illegal value.
              > 0:  if CBDSQR did not converge, INFO specifies how many
                    superdiagonals of an intermediate bidiagonal form B
                    did not converge to zero. See the description of RWORK
                    above for details.

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Definition at line 212 of file cgesvd.f.

Author

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