slalsd.f (3)  Linux Manuals
NAME
slalsd.f 
SYNOPSIS
Functions/Subroutines
subroutine slalsd (UPLO, SMLSIZ, N, NRHS, D, E, B, LDB, RCOND, RANK, WORK, IWORK, INFO)
SLALSD uses the singular value decomposition of A to solve the least squares problem.
Function/Subroutine Documentation
subroutine slalsd (characterUPLO, integerSMLSIZ, integerN, integerNRHS, real, dimension( * )D, real, dimension( * )E, real, dimension( ldb, * )B, integerLDB, realRCOND, integerRANK, real, dimension( * )WORK, integer, dimension( * )IWORK, integerINFO)
SLALSD uses the singular value decomposition of A to solve the least squares problem.
Purpose:

SLALSD uses the singular value decomposition of A to solve the least squares problem of finding X to minimize the Euclidean norm of each column of A*XB, where A is NbyN upper bidiagonal, and X and B are NbyNRHS. The solution X overwrites B. The singular values of A smaller than RCOND times the largest singular value are treated as zero in solving the least squares problem; in this case a minimum norm solution is returned. The actual singular values are returned in D in ascending order. This code makes very mild assumptions about floating point arithmetic. It will work on machines with a guard digit in add/subtract, or on those binary machines without guard digits which subtract like the Cray XMP, Cray YMP, Cray C 90, or Cray 2. It could conceivably fail on hexadecimal or decimal machines without guard digits, but we know of none.
Parameters:

UPLO
UPLO is CHARACTER*1 = 'U': D and E define an upper bidiagonal matrix. = 'L': D and E define a lower bidiagonal matrix.
SMLSIZSMLSIZ is INTEGER The maximum size of the subproblems at the bottom of the computation tree.
NN is INTEGER The dimension of the bidiagonal matrix. N >= 0.
NRHSNRHS is INTEGER The number of columns of B. NRHS must be at least 1.
DD is REAL array, dimension (N) On entry D contains the main diagonal of the bidiagonal matrix. On exit, if INFO = 0, D contains its singular values.
EE is REAL array, dimension (N1) Contains the superdiagonal entries of the bidiagonal matrix. On exit, E has been destroyed.
BB is REAL array, dimension (LDB,NRHS) On input, B contains the right hand sides of the least squares problem. On output, B contains the solution X.
LDBLDB is INTEGER The leading dimension of B in the calling subprogram. LDB must be at least max(1,N).
RCONDRCOND is REAL The singular values of A less than or equal to RCOND times the largest singular value are treated as zero in solving the least squares problem. If RCOND is negative, machine precision is used instead. For example, if diag(S)*X=B were the least squares problem, where diag(S) is a diagonal matrix of singular values, the solution would be X(i) = B(i) / S(i) if S(i) is greater than RCOND*max(S), and X(i) = 0 if S(i) is less than or equal to RCOND*max(S).
RANKRANK is INTEGER The number of singular values of A greater than RCOND times the largest singular value.
WORKWORK is REAL array, dimension at least (9*N + 2*N*SMLSIZ + 8*N*NLVL + N*NRHS + (SMLSIZ+1)**2), where NLVL = max(0, INT(log_2 (N/(SMLSIZ+1))) + 1).
IWORKIWORK is INTEGER array, dimension at least (3*N*NLVL + 11*N)
INFOINFO is INTEGER = 0: successful exit. < 0: if INFO = i, the ith argument had an illegal value. > 0: The algorithm failed to compute a singular value while working on the submatrix lying in rows and columns INFO/(N+1) through MOD(INFO,N+1).
Author:

Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
 September 2012
Contributors:

Ming Gu and RenCang Li, Computer Science Division, University of California at Berkeley, USA
Osni Marques, LBNL/NERSC, USA
Definition at line 179 of file slalsd.f.
Author
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