# zgsvj0.f - Man Page

SRC/zgsvj0.f

## Synopsis

### Functions/Subroutines

subroutine zgsvj0 (jobv, m, n, a, lda, d, sva, mv, v, ldv, eps, sfmin, tol, nsweep, work, lwork, info)
ZGSVJ0 pre-processor for the routine zgesvj.

## Function/Subroutine Documentation

### subroutine zgsvj0 (character*1 jobv, integer m, integer n, complex*16, dimension( lda, * ) a, integer lda, complex*16, dimension( n ) d, double precision, dimension( n ) sva, integer mv, complex*16, dimension( ldv, * ) v, integer ldv, double precision eps, double precision sfmin, double precision tol, integer nsweep, complex*16, dimension( lwork ) work, integer lwork, integer info)

ZGSVJ0 pre-processor for the routine zgesvj.

Purpose:

``` ZGSVJ0 is called from ZGESVJ as a pre-processor and that is its main
purpose. It applies Jacobi rotations in the same way as ZGESVJ does, but
it does not check convergence (stopping criterion). Few tuning
parameters (marked by [TP]) are available for the implementer.```
Parameters

JOBV

```          JOBV is CHARACTER*1
Specifies whether the output from this procedure is used
to compute the matrix V:
= 'V': the product of the Jacobi rotations is accumulated
by postmultiplying the N-by-N array V.
(See the description of V.)
= 'A': the product of the Jacobi rotations is accumulated
by postmultiplying the MV-by-N array V.
(See the descriptions of MV and V.)
= 'N': the Jacobi rotations are not accumulated.```

M

```          M is INTEGER
The number of rows of the input matrix A.  M >= 0.```

N

```          N is INTEGER
The number of columns of the input matrix A.
M >= N >= 0.```

A

```          A is COMPLEX*16 array, dimension (LDA,N)
On entry, M-by-N matrix A, such that A*diag(D) represents
the input matrix.
On exit,
A_onexit * diag(D_onexit) represents the input matrix A*diag(D)
post-multiplied 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 D, TOL and NSWEEP.)```

LDA

```          LDA is INTEGER
The leading dimension of the array A.  LDA >= max(1,M).```

D

```          D is COMPLEX*16 array, dimension (N)
The array D accumulates the scaling factors from the complex scaled
Jacobi rotations.
On entry, A*diag(D) represents the input matrix.
On exit, A_onexit*diag(D_onexit) represents the input matrix
post-multiplied 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 A, TOL and NSWEEP.)```

SVA

```          SVA is DOUBLE PRECISION 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 A_onexit*diag(D_onexit).```

MV

```          MV is INTEGER
If JOBV = 'A', then MV rows of V are post-multiplied by a
sequence of Jacobi rotations.
If JOBV = 'N',   then MV is not referenced.```

V

```          V is COMPLEX*16 array, dimension (LDV,N)
If JOBV = 'V' then N rows of V are post-multiplied by a
sequence of Jacobi rotations.
If JOBV = 'A' then MV rows of V are post-multiplied by a
sequence of Jacobi rotations.
If JOBV = 'N',   then V is not referenced.```

LDV

```          LDV is INTEGER
The leading dimension of the array V,  LDV >= 1.
If JOBV = 'V', LDV >= N.
If JOBV = 'A', LDV >= MV.```

EPS

```          EPS is DOUBLE PRECISION
EPS = DLAMCH('Epsilon')```

SFMIN

```          SFMIN is DOUBLE PRECISION
SFMIN = DLAMCH('Safe Minimum')```

TOL

```          TOL is DOUBLE PRECISION
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)))) > TOL.```

NSWEEP

```          NSWEEP is INTEGER
NSWEEP is the number of sweeps of Jacobi rotations to be
performed.```

WORK

`          WORK is COMPLEX*16 array, dimension (LWORK)`

LWORK

```          LWORK is INTEGER
LWORK is the dimension of WORK. LWORK >= M.```

INFO

```          INFO is INTEGER
= 0:  successful exit.
< 0:  if INFO = -i, then the i-th argument had an illegal value```
Author

Univ. of Tennessee

Univ. of California Berkeley

NAG Ltd.

Further Details:

ZGSVJ0 is used just to enable ZGESVJ to call a simplified version of itself to work on a submatrix of the original matrix.

Contributor: Zlatko Drmac (Zagreb, Croatia)

Please report all bugs and send interesting test examples and comments to drmac@math.hr. Thank you.

Definition at line 216 of file zgsvj0.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

The man page zgsvj0(3) is an alias of zgsvj0.f(3).

Tue Nov 28 2023 12:08:42 Version 3.12.0 LAPACK