# dlaqsy.f man page

dlaqsy.f —

## Synopsis

### Functions/Subroutines

subroutinedlaqsy(UPLO, N, A, LDA, S, SCOND, AMAX, EQUED)DLAQSYscales a symmetric/Hermitian matrix, using scaling factors computed by spoequ.

## Function/Subroutine Documentation

### subroutine dlaqsy (characterUPLO, integerN, double precision, dimension( lda, * )A, integerLDA, double precision, dimension( * )S, double precisionSCOND, double precisionAMAX, characterEQUED)

**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= 'Y': Equilibration was done, i.e., A has been replaced by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:**

September 2012

Definition at line 134 of file dlaqsy.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

dlaqsy(3) is an alias of dlaqsy.f(3).