slals0 (l)  Linux Man Pages
slals0: applies back the multiplying factors of either the left or the right singular vector matrix of a diagonal matrix appended by a row to the right hand side matrix B in solving the least squares problem using the divideandconquer SVD approach
NAME
SLALS0  applies back the multiplying factors of either the left or the right singular vector matrix of a diagonal matrix appended by a row to the right hand side matrix B in solving the least squares problem using the divideandconquer SVD approachSYNOPSIS
 SUBROUTINE SLALS0(
 ICOMPQ, NL, NR, SQRE, NRHS, B, LDB, BX, LDBX, PERM, GIVPTR, GIVCOL, LDGCOL, GIVNUM, LDGNUM, POLES, DIFL, DIFR, Z, K, C, S, WORK, INFO )
 INTEGER GIVPTR, ICOMPQ, INFO, K, LDB, LDBX, LDGCOL, LDGNUM, NL, NR, NRHS, SQRE
 REAL C, S
 INTEGER GIVCOL( LDGCOL, * ), PERM( * )
 REAL B( LDB, * ), BX( LDBX, * ), DIFL( * ), DIFR( LDGNUM, * ), GIVNUM( LDGNUM, * ), POLES( LDGNUM, * ), WORK( * ), Z( * )
PURPOSE
SLALS0 applies back the multiplying factors of either the left or the right singular vector matrix of a diagonal matrix appended by a row to the right hand side matrix B in solving the least squares problem using the divideandconquer SVD approach. For the left singular vector matrix, three types of orthogonal matrices are involved:(1L) Givens rotations: the number of such rotations is GIVPTR; the
(3L) The left singular vector matrix of the remaining matrix. For the right singular vector matrix, four types of orthogonal matrices are involved:
(1R) The right singular vector matrix of the remaining matrix. (2R) If SQRE = 1, one extra Givens rotation to generate the right
(3R) The inverse transformation of (2L).
(4R) The inverse transformation of (1L).
ARGUMENTS
ICOMPQ (input) INTEGER Specifies whether singular vectors are to be computed in factored form:= 0: Left singular vector matrix.
= 1: Right singular vector matrix.
 NL (input) INTEGER
 The row dimension of the upper block. NL >= 1.
 NR (input) INTEGER
 The row dimension of the lower block. NR >= 1.
 SQRE (input) INTEGER

= 0: the lower block is an NRbyNR square matrix.
= 1: the lower block is an NRby(NR+1) rectangular matrix. The bidiagonal matrix has row dimension N = NL + NR + 1, and column dimension M = N + SQRE.  NRHS (input) INTEGER
 The number of columns of B and BX. NRHS must be at least 1.
 B (input/output) REAL 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. LDB must be at least max(1,MAX( M, N ) ).
 BX (workspace) REAL array, dimension ( LDBX, NRHS )
 LDBX (input) INTEGER
 The leading dimension of BX.
 PERM (input) INTEGER array, dimension ( N )
 The permutations (from deflation and sorting) applied to the two blocks. GIVPTR (input) INTEGER The number of Givens rotations which took place in this subproblem. GIVCOL (input) INTEGER array, dimension ( LDGCOL, 2 ) Each pair of numbers indicates a pair of rows/columns involved in a Givens rotation. LDGCOL (input) INTEGER The leading dimension of GIVCOL, must be at least N. GIVNUM (input) REAL array, dimension ( LDGNUM, 2 ) Each number indicates the C or S value used in the corresponding Givens rotation. LDGNUM (input) INTEGER The leading dimension of arrays DIFR, POLES and GIVNUM, must be at least K.
 POLES (input) REAL array, dimension ( LDGNUM, 2 )
 On entry, POLES(1:K, 1) contains the new singular values obtained from solving the secular equation, and POLES(1:K, 2) is an array containing the poles in the secular equation.
 DIFL (input) REAL array, dimension ( K ).
 On entry, DIFL(I) is the distance between Ith updated (undeflated) singular value and the Ith (undeflated) old singular value.
 DIFR (input) REAL array, dimension ( LDGNUM, 2 ).
 On entry, DIFR(I, 1) contains the distances between Ith updated (undeflated) singular value and the I+1th (undeflated) old singular value. And DIFR(I, 2) is the normalizing factor for the Ith right singular vector.
 Z (input) REAL array, dimension ( K )
 Contain the components of the deflationadjusted updating row vector.
 K (input) INTEGER
 Contains the dimension of the nondeflated matrix, This is the order of the related secular equation. 1 <= K <=N.
 C (input) REAL
 C contains garbage if SQRE =0 and the Cvalue of a Givens rotation related to the right null space if SQRE = 1.
 S (input) REAL
 S contains garbage if SQRE =0 and the Svalue of a Givens rotation related to the right null space if SQRE = 1.
 WORK (workspace) REAL array, dimension ( K )
 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