DLASD0(3S)DLASD0(3S)NAMEDLASD0 - 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
SYNOPSIS
SUBROUTINE DLASD0( N, SQRE, D, E, U, LDU, VT, LDVT, SMLSIZ, IWORK, WORK,
INFO )
INTEGER INFO, LDU, LDVT, N, SMLSIZ, SQRE
INTEGER IWORK( * )
DOUBLE PRECISION D( * ), E( * ), U( LDU, * ), VT( LDVT, * ),
WORK( * )
IMPLEMENTATION
These routines are part of the SCSL Scientific Library and can be loaded
using either the -lscs or the -lscs_mp option. The -lscs_mp option
directs the linker to use the multi-processor version of the library.
When linking to SCSL with -lscs or -lscs_mp, the default integer size is
4 bytes (32 bits). Another version of SCSL is available in which integers
are 8 bytes (64 bits). This version allows the user access to larger
memory sizes and helps when porting legacy Cray codes. It can be loaded
by using the -lscs_i8 option or the -lscs_i8_mp option. A program may use
only one of the two versions; 4-byte integer and 8-byte integer library
calls cannot be mixed.
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.
ARGUMENTS
N (input) INTEGER
On entry, the row dimension of the upper bidiagonal matrix. This
is also the dimension of the main diagonal array D.
SQRE (input) 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;
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DLASD0(3S)DLASD0(3S)
D (input/output) 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 (input) DOUBLE PRECISION array, dimension (M-1)
Contains the subdiagonal entries of the bidiagonal matrix. On
exit, E has been destroyed.
U (output) DOUBLE PRECISION array, dimension at least (LDQ, N)
On exit, U contains the left singular vectors.
LDU (input) INTEGER
On entry, leading dimension of U.
VT (output) DOUBLE PRECISION array, dimension at least (LDVT, M)
On exit, VT' contains the right singular vectors.
LDVT (input) INTEGER
On entry, leading dimension of VT.
SMLSIZ (input) INTEGER On entry, maximum size of the subproblems
at the bottom of the computation tree.
IWORK (workspace) INTEGER array.
Dimension must be at least (8 * N)
WORK (workspace) DOUBLE PRECISION array.
Dimension must be at least (3 * M**2 + 2 * M)
INFO (output) INTEGER
= 0: successful exit.
< 0: if INFO = -i, the i-th argument had an illegal value.
> 0: if INFO = 1, an singular value did not converge
FURTHER DETAILS
Based on contributions by
Ming Gu and Huan Ren, Computer Science Division, University of
California at Berkeley, USA
SEE ALSOINTRO_LAPACK(3S), INTRO_SCSL(3S)
This man page is available only online.
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