zsyequb (l)  Linux Manuals
zsyequb: computes row and column scalings intended to equilibrate a symmetric matrix A and reduce its condition number (with respect to the twonorm)
Command to display zsyequb
manual in Linux: $ man l zsyequb
NAME
ZSYEQUB  computes row and column scalings intended to equilibrate a symmetric matrix A and reduce its condition number (with respect to the twonorm)
SYNOPSIS
 SUBROUTINE ZSYEQUB(

UPLO, N, A, LDA, S, SCOND, AMAX, WORK, INFO )

IMPLICIT
NONE

INTEGER
INFO, LDA, N

DOUBLE
PRECISION AMAX, SCOND

CHARACTER
UPLO

COMPLEX*16
A( LDA, * ), WORK( * )

DOUBLE
PRECISION S( * )
PURPOSE
ZSYEQUB computes row and column scalings intended to equilibrate a
symmetric matrix A and reduce its condition number
(with respect to the twonorm). S contains the scale factors,
S(i) = 1/sqrt(A(i,i)), chosen so that the scaled matrix B with
elements B(i,j) = S(i)*A(i,j)*S(j) has ones on the diagonal. This
choice of S puts the condition number of B within a factor N of the
smallest possible condition number over all possible diagonal
scalings.
ARGUMENTS
 N (input) INTEGER

The order of the matrix A. N >= 0.
 A (input) COMPLEX*16 array, dimension (LDA,N)

The NbyN symmetric matrix whose scaling
factors are to be computed. Only the diagonal elements of A
are referenced.
 LDA (input) INTEGER

The leading dimension of the array A. LDA >= max(1,N).
 S (output) DOUBLE PRECISION array, dimension (N)

If INFO = 0, S contains the scale factors for A.
 SCOND (output) DOUBLE PRECISION

If INFO = 0, S contains the ratio of the smallest S(i) to
the largest S(i). If SCOND >= 0.1 and AMAX is neither too
large nor too small, it is not worth scaling by S.
 AMAX (output) DOUBLE PRECISION

Absolute value of largest matrix element. If AMAX is very
close to overflow or very close to underflow, the matrix
should be scaled.
INFO (output) INTEGER
= 0: successful exit
< 0: if INFO = i, the ith argument had an illegal value
> 0: if INFO = i, the ith diagonal element is nonpositive.
Pages related to zsyequb
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