dlasd0 (3)

Functions/Subroutines

subroutine dlasd0 (N, SQRE, D, E, U, LDU, VT, LDVT, SMLSIZ, IWORK, WORK, INFO)

DLASD0 computes the singular values of a real upper bidiagonal n-by-m matrix B with diagonal d and off-diagonal e. Used by sbdsdc.

subroutine dlasd0 (integerN, integerSQRE, double precision, dimension( * )D, double precision, dimension( * )E, double precision, dimension( ldu, * )U, integerLDU, double precision, dimension( ldvt, * )VT, integerLDVT, integerSMLSIZ, integer, dimension( * )IWORK, double precision, dimension( * )WORK, integerINFO)

DLASD0 computes the singular values of a real upper bidiagonal n-by-m matrix B with diagonal d and off-diagonal e. Used by sbdsdc.

Purpose:

 Using a divide and conquer approach, DLASD0 computes the singular
 value decomposition (SVD) of a real upper bidiagonal N-by-M
 matrix B with diagonal D and offdiagonal E, where M = N + SQRE.
 The algorithm computes orthogonal matrices U and VT such that
 B = U * S * VT. The singular values S are overwritten on D.

 A related subroutine, DLASDA, computes only the singular values,
 and optionally, the singular vectors in compact form.

Parameters:

N

          N is INTEGER
         On entry, the row dimension of the upper bidiagonal matrix.
         This is also the dimension of the main diagonal array D.

SQRE

          SQRE is INTEGER
         Specifies the column dimension of the bidiagonal matrix.
         = 0: The bidiagonal matrix has column dimension M = N;
         = 1: The bidiagonal matrix has column dimension M = N+1;

D

          D is DOUBLE PRECISION array, dimension (N)
         On entry D contains the main diagonal of the bidiagonal
         matrix.
         On exit D, if INFO = 0, contains its singular values.

E

          E is DOUBLE PRECISION array, dimension (M-1)
         Contains the subdiagonal entries of the bidiagonal matrix.
         On exit, E has been destroyed.

U

          U is DOUBLE PRECISION array, dimension at least (LDQ, N)
         On exit, U contains the left singular vectors.

LDU

          LDU is INTEGER
         On entry, leading dimension of U.

VT

          VT is DOUBLE PRECISION array, dimension at least (LDVT, M)
         On exit, VT**T contains the right singular vectors.

LDVT

          LDVT is INTEGER
         On entry, leading dimension of VT.

SMLSIZ

          SMLSIZ is INTEGER
         On entry, maximum size of the subproblems at the
         bottom of the computation tree.

IWORK

          IWORK is INTEGER work array.
         Dimension must be at least (8 * N)

WORK

          WORK is DOUBLE PRECISION work array.
         Dimension must be at least (3 * M**2 + 2 * M)

INFO

          INFO is INTEGER
          = 0:  successful exit.
          < 0:  if INFO = -i, the i-th argument had an illegal value.
          > 0:  if INFO = 1, a singular value did not converge

Author:

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Date:

September 2012

Contributors:

Ming Gu and Huan Ren, Computer Science Division, University of California at Berkeley, USA

Definition at line 152 of file dlasd0.f.

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