dlalsa (l)  Linux Man Pages
dlalsa: is an itermediate step in solving the least squares problem by computing the SVD of the coefficient matrix in compact form (The singular vectors are computed as products of simple orthorgonal matrices.)
NAME
DLALSA  is an itermediate step in solving the least squares problem by computing the SVD of the coefficient matrix in compact form (The singular vectors are computed as products of simple orthorgonal matrices.)SYNOPSIS
 SUBROUTINE DLALSA(
 ICOMPQ, SMLSIZ, N, NRHS, B, LDB, BX, LDBX, U, LDU, VT, K, DIFL, DIFR, Z, POLES, GIVPTR, GIVCOL, LDGCOL, PERM, GIVNUM, C, S, WORK, IWORK, INFO )
 INTEGER ICOMPQ, INFO, LDB, LDBX, LDGCOL, LDU, N, NRHS, SMLSIZ
 INTEGER GIVCOL( LDGCOL, * ), GIVPTR( * ), IWORK( * ), K( * ), PERM( LDGCOL, * )
 DOUBLE PRECISION B( LDB, * ), BX( LDBX, * ), C( * ), DIFL( LDU, * ), DIFR( LDU, * ), GIVNUM( LDU, * ), POLES( LDU, * ), S( * ), U( LDU, * ), VT( LDU, * ), WORK( * ), Z( LDU, * )
PURPOSE
DLALSA is an itermediate step in solving the least squares problem by computing the SVD of the coefficient matrix in compact form (The singular vectors are computed as products of simple orthorgonal matrices.). If ICOMPQ = 0, DLALSA applies the inverse of the left singular vector matrix of an upper bidiagonal matrix to the right hand side; and if ICOMPQ = 1, DLALSA applies the right singular vector matrix to the right hand side. The singular vector matrices were generated in compact form by DLALSA.ARGUMENTS
ICOMPQ (input) INTEGER Specifies whether the left or the right singular vector matrix is involved. = 0: Left singular vector matrix= 1: Right singular vector matrix SMLSIZ (input) INTEGER The maximum size of the subproblems at the bottom of the computation tree.
 N (input) INTEGER
 The row and column dimensions of the upper bidiagonal matrix.
 NRHS (input) INTEGER
 The number of columns of B and BX. NRHS must be at least 1.
 B (input/output) DOUBLE PRECISION array, dimension ( LDB, NRHS )
 On input, B contains the right hand sides of the least squares problem in rows 1 through M. On output, B contains the solution X in rows 1 through N.
 LDB (input) INTEGER
 The leading dimension of B in the calling subprogram. LDB must be at least max(1,MAX( M, N ) ).
 BX (output) DOUBLE PRECISION array, dimension ( LDBX, NRHS )
 On exit, the result of applying the left or right singular vector matrix to B.
 LDBX (input) INTEGER
 The leading dimension of BX.
 U (input) DOUBLE PRECISION array, dimension ( LDU, SMLSIZ ).
 On entry, U contains the left singular vector matrices of all subproblems at the bottom level.
 LDU (input) INTEGER, LDU = > N.
 The leading dimension of arrays U, VT, DIFL, DIFR, POLES, GIVNUM, and Z.
 VT (input) DOUBLE PRECISION array, dimension ( LDU, SMLSIZ+1 ).
 On entry, VTaq contains the right singular vector matrices of all subproblems at the bottom level.
 K (input) INTEGER array, dimension ( N ).
 DIFL (input) DOUBLE PRECISION array, dimension ( LDU, NLVL ).
 where NLVL = INT(log_2 (N/(SMLSIZ+1))) + 1.
 DIFR (input) DOUBLE PRECISION array, dimension ( LDU, 2 * NLVL ).
 On entry, DIFL(*, I) and DIFR(*, 2 * I 1) record distances between singular values on the Ith level and singular values on the (I 1)th level, and DIFR(*, 2 * I) record the normalizing factors of the right singular vectors matrices of subproblems on Ith level.
 Z (input) DOUBLE PRECISION array, dimension ( LDU, NLVL ).
 On entry, Z(1, I) contains the components of the deflation adjusted updating row vector for subproblems on the Ith level.
 POLES (input) DOUBLE PRECISION array, dimension ( LDU, 2 * NLVL ).
 On entry, POLES(*, 2 * I 1: 2 * I) contains the new and old singular values involved in the secular equations on the Ith level. GIVPTR (input) INTEGER array, dimension ( N ). On entry, GIVPTR( I ) records the number of Givens rotations performed on the Ith problem on the computation tree. GIVCOL (input) INTEGER array, dimension ( LDGCOL, 2 * NLVL ). On entry, for each I, GIVCOL(*, 2 * I  1: 2 * I) records the locations of Givens rotations performed on the Ith level on the computation tree. LDGCOL (input) INTEGER, LDGCOL = > N. The leading dimension of arrays GIVCOL and PERM.
 PERM (input) INTEGER array, dimension ( LDGCOL, NLVL ).
 On entry, PERM(*, I) records permutations done on the Ith level of the computation tree. GIVNUM (input) DOUBLE PRECISION array, dimension ( LDU, 2 * NLVL ). On entry, GIVNUM(*, 2 *I 1 : 2 * I) records the C and S values of Givens rotations performed on the Ith level on the computation tree.
 C (input) DOUBLE PRECISION array, dimension ( N ).
 On entry, if the Ith subproblem is not square, C( I ) contains the Cvalue of a Givens rotation related to the right null space of the Ith subproblem.
 S (input) DOUBLE PRECISION array, dimension ( N ).
 On entry, if the Ith subproblem is not square, S( I ) contains the Svalue of a Givens rotation related to the right null space of the Ith subproblem.
 WORK (workspace) DOUBLE PRECISION array.
 The dimension must be at least N.
 IWORK (workspace) INTEGER array.
 The dimension must be at least 3 * N
 INFO (output) INTEGER

= 0: successful exit.
< 0: if INFO = i, the ith argument had an illegal value.
FURTHER DETAILS
Based on contributions byMing Gu and RenCang Li, Computer Science Division, University of
Osni Marques, LBNL/NERSC, USA