dsyequb (l)  Linux Man Pages
dsyequb: 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 dsyequb
manual in Linux: $ man l dsyequb
NAME
DSYEQUB  computes row and column scalings intended to equilibrate a symmetric matrix A and reduce its condition number (with respect to the twonorm)
SYNOPSIS
 SUBROUTINE DSYEQUB(

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

IMPLICIT
NONE

INTEGER
INFO, LDA, N

DOUBLE
PRECISION AMAX, SCOND

CHARACTER
UPLO

DOUBLE
PRECISION A( LDA, * ), S( * ), WORK( * )
PURPOSE
DSYEQUB 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) DOUBLE PRECISION 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 dsyequb
 dsyequb (3)
 dsyev (l)  computes all eigenvalues and, optionally, eigenvectors of a real symmetric matrix A
 dsyevd (l)  computes all eigenvalues and, optionally, eigenvectors of a real symmetric matrix A
 dsyevr (l)  computes selected eigenvalues and, optionally, eigenvectors of a real symmetric matrix A
 dsyevx (l)  computes selected eigenvalues and, optionally, eigenvectors of a real symmetric matrix A
 dsycon (l)  estimates the reciprocal of the condition number (in the 1norm) of a real symmetric matrix A using the factorization A = U*D*U**T or A = L*D*L**T computed by DSYTRF
 dsygs2 (l)  reduces a real symmetricdefinite generalized eigenproblem to standard form
 dsygst (l)  reduces a real symmetricdefinite generalized eigenproblem to standard form