sgsvj1 (l)  Linux Man Pages
sgsvj1: is called from SGESVJ as a preprocessor and that is its main purpose
NAME
SGSVJ1  is called from SGESVJ as a preprocessor and that is its main purposeSYNOPSIS
 SUBROUTINE SGSVJ1(
 JOBV, M, N, N1, A, LDA, D, SVA, MV, V, LDV,
 + EPS, SFMIN, TOL, NSWEEP, WORK, LWORK, INFO )
 IMPLICIT NONE
 REAL EPS, SFMIN, TOL
 INTEGER INFO, LDA, LDV, LWORK, M, MV, N, N1, NSWEEP
 CHARACTER*1 JOBV
 REAL A( LDA, * ), D( N ), SVA( N ), V( LDV, * ),
 + WORK( LWORK )
PURPOSE
SGSVJ1 is called from SGESVJ as a preprocessor and that is its main purpose. It applies Jacobi rotations in the same way as SGESVJ does, but it targets only particular pivots and it does not check convergence (stopping criterion). Few tunning parameters (marked by [TP]) are available for the implementer.Further Details
SGSVJ1 applies few sweeps of Jacobi rotations in the column space of the input MbyN matrix A. The pivot pairs are taken from the (1,2) offdiagonal block in the corresponding NbyN Gram matrix A^T * A. The blockentries (tiles) of the (1,2) offdiagonal block are marked by the [x]aqs in the following scheme:



[x]
[x]
[x]
In terms of the columns of A, the first N1 columns are rotated aqagainstaq the remaining NN1 columns, trying to increase the angle between the corresponding subspaces. The offdiagonal block is N1by(NN1) and it is tiled using quadratic tiles of side KBL. Here, KBL is a tunning parmeter. The number of sweeps is given in NSWEEP and the orthogonality threshold is given in TOL.
Contributors
~~~~~~~~~~~~
Zlatko Drmac (Zagreb, Croatia) and Kresimir Veselic (Hagen, Germany)
ARGUMENTS
 JOBV (input) CHARACTER*1

Specifies whether the output from this procedure is used
to compute the matrix V:
= aqVaq: the product of the Jacobi rotations is accumulated by postmulyiplying the NbyN array V. (See the description of V.) = aqAaq: the product of the Jacobi rotations is accumulated by postmulyiplying the MVbyN array V. (See the descriptions of MV and V.) = aqNaq: the Jacobi rotations are not accumulated.  M (input) INTEGER
 The number of rows of the input matrix A. M >= 0.
 N (input) INTEGER
 The number of columns of the input matrix A. M >= N >= 0.
 N1 (input) INTEGER
 N1 specifies the 2 x 2 block partition, the first N1 columns are rotated aqagainstaq the remaining NN1 columns of A.
 A (input/output) REAL array, dimension (LDA,N)
 On entry, MbyN matrix A, such that A*diag(D) represents the input matrix. On exit, A_onexit * D_onexit represents the input matrix A*diag(D) postmultiplied by a sequence of Jacobi rotations, where the rotation threshold and the total number of sweeps are given in TOL and NSWEEP, respectively. (See the descriptions of N1, D, TOL and NSWEEP.)
 LDA (input) INTEGER
 The leading dimension of the array A. LDA >= max(1,M).
 D (input/workspace/output) REAL array, dimension (N)
 The array D accumulates the scaling factors from the fast scaled Jacobi rotations. On entry, A*diag(D) represents the input matrix. On exit, A_onexit*diag(D_onexit) represents the input matrix postmultiplied by a sequence of Jacobi rotations, where the rotation threshold and the total number of sweeps are given in TOL and NSWEEP, respectively. (See the descriptions of N1, A, TOL and NSWEEP.)
 SVA (input/workspace/output) REAL array, dimension (N)
 On entry, SVA contains the Euclidean norms of the columns of the matrix A*diag(D). On exit, SVA contains the Euclidean norms of the columns of the matrix onexit*diag(D_onexit).
 MV (input) INTEGER
 If JOBV .EQ. aqAaq, then MV rows of V are postmultipled by a sequence of Jacobi rotations. If JOBV = aqNaq, then MV is not referenced.
 V (input/output) REAL array, dimension (LDV,N)
 If JOBV .EQ. aqVaq then N rows of V are postmultipled by a sequence of Jacobi rotations. If JOBV .EQ. aqAaq then MV rows of V are postmultipled by a sequence of Jacobi rotations. If JOBV = aqNaq, then V is not referenced.
 LDV (input) INTEGER
 The leading dimension of the array V, LDV >= 1. If JOBV = aqVaq, LDV .GE. N. If JOBV = aqAaq, LDV .GE. MV.
 EPS (input) INTEGER
 EPS = SLAMCH(aqEpsilonaq)
 SFMIN (input) INTEGER
 SFMIN = SLAMCH(aqSafe Minimumaq)
 TOL (input) REAL

TOL is the threshold for Jacobi rotations. For a pair
A(:,p), A(:,q) of pivot columns, the Jacobi rotation is
applied only if ABS(COS(angle(A(:,p),A(:,q)))) .GT. TOL.  NSWEEP (input) INTEGER
 NSWEEP is the number of sweeps of Jacobi rotations to be performed.
 WORK (workspace) REAL array, dimension LWORK.
 LWORK (input) INTEGER
 LWORK is the dimension of WORK. LWORK .GE. M.
 INFO (output) INTEGER

= 0 : successful exit.
< 0 : if INFO = i, then the ith argument had an illegal value