# dlaqsy.f - Man Page

## Synopsis

### Functions/Subroutines

subroutine **dlaqsy** (UPLO, **N**, A, **LDA**, S, SCOND, AMAX, EQUED)**DLAQSY** scales a symmetric/Hermitian matrix, using scaling factors computed by spoequ.

## Function/Subroutine Documentation

### subroutine dlaqsy (character UPLO, integer N, double precision, dimension( lda, * ) A, integer LDA, double precision, dimension( * ) S, double precision SCOND, double precision AMAX, character EQUED)

**DLAQSY** scales a symmetric/Hermitian matrix, using scaling factors computed by spoequ.

**Purpose:**

DLAQSY equilibrates a symmetric matrix A using the scaling factors in the vector S.

**Parameters:***UPLO*UPLO is CHARACTER*1 Specifies whether the upper or lower triangular part of the symmetric matrix A is stored. = 'U': Upper triangular = 'L': Lower triangular

*N*N is INTEGER The order of the matrix A. N >= 0.

*A*A is DOUBLE PRECISION array, dimension (LDA,N) On entry, the symmetric matrix A. If UPLO = 'U', the leading n by n upper triangular part of A contains the upper triangular part of the matrix A, and the strictly lower triangular part of A is not referenced. If UPLO = 'L', the leading n by n lower triangular part of A contains the lower triangular part of the matrix A, and the strictly upper triangular part of A is not referenced. On exit, if EQUED = 'Y', the equilibrated matrix: diag(S) * A * diag(S).

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

*S*S is DOUBLE PRECISION array, dimension (N) The scale factors for A.

*SCOND*SCOND is DOUBLE PRECISION Ratio of the smallest S(i) to the largest S(i).

*AMAX*AMAX is DOUBLE PRECISION Absolute value of largest matrix entry.

*EQUED*EQUED is CHARACTER*1 Specifies whether or not equilibration was done. = 'N': No equilibration. = 'Y': Equilibration was done, i.e., A has been replaced by diag(S) * A * diag(S).

**Internal Parameters:**

THRESH is a threshold value used to decide if scaling should be done based on the ratio of the scaling factors. If SCOND < THRESH, scaling is done. LARGE and SMALL are threshold values used to decide if scaling should be done based on the absolute size of the largest matrix element. If AMAX > LARGE or AMAX < SMALL, scaling is done.

**Author:**Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

**Date:**December 2016

Definition at line 135 of file dlaqsy.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

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

Tue Nov 14 2017 Version 3.8.0 LAPACK