# sla_syamv.f man page

sla_syamv.f —

## Synopsis

### Functions/Subroutines

subroutinesla_syamv(UPLO, N, ALPHA, A, LDA, X, INCX, BETA, Y, INCY)SLA_SYAMVcomputes a matrix-vector product using a symmetric indefinite matrix to calculate error bounds.

## Function/Subroutine Documentation

### subroutine sla_syamv (integerUPLO, integerN, realALPHA, real, dimension( lda, * )A, integerLDA, real, dimension( * )X, integerINCX, realBETA, real, dimension( * )Y, integerINCY)

**SLA_SYAMV** computes a matrix-vector product using a symmetric indefinite matrix to calculate error bounds.

**Purpose:**

```
SLA_SYAMV performs the matrix-vector operation
y := alpha*abs(A)*abs(x) + beta*abs(y),
where alpha and beta are scalars, x and y are vectors and A is an
n by n symmetric matrix.
This function is primarily used in calculating error bounds.
To protect against underflow during evaluation, components in
the resulting vector are perturbed away from zero by (N+1)
times the underflow threshold. To prevent unnecessarily large
errors for block-structure embedded in general matrices,
"symbolically" zero components are not perturbed. A zero
entry is considered "symbolic" if all multiplications involved
in computing that entry have at least one zero multiplicand.
```

**Parameters:**

*UPLO*

```
UPLO is INTEGER
On entry, UPLO specifies whether the upper or lower
triangular part of the array A is to be referenced as
follows:
UPLO = BLAS_UPPER Only the upper triangular part of A
is to be referenced.
UPLO = BLAS_LOWER Only the lower triangular part of A
is to be referenced.
Unchanged on exit.
```

*N*

```
N is INTEGER
On entry, N specifies the number of columns of the matrix A.
N must be at least zero.
Unchanged on exit.
```

*ALPHA*

```
ALPHA is REAL .
On entry, ALPHA specifies the scalar alpha.
Unchanged on exit.
```

*A*

```
A is REAL array of DIMENSION ( LDA, n ).
Before entry, the leading m by n part of the array A must
contain the matrix of coefficients.
Unchanged on exit.
```

*LDA*

```
LDA is INTEGER
On entry, LDA specifies the first dimension of A as declared
in the calling (sub) program. LDA must be at least
max( 1, n ).
Unchanged on exit.
```

*X*

```
X is REAL array, dimension
( 1 + ( n - 1 )*abs( INCX ) )
Before entry, the incremented array X must contain the
vector x.
Unchanged on exit.
```

*INCX*

```
INCX is INTEGER
On entry, INCX specifies the increment for the elements of
X. INCX must not be zero.
Unchanged on exit.
```

*BETA*

```
BETA is REAL .
On entry, BETA specifies the scalar beta. When BETA is
supplied as zero then Y need not be set on input.
Unchanged on exit.
```

*Y*

```
Y is REAL array, dimension
( 1 + ( n - 1 )*abs( INCY ) )
Before entry with BETA non-zero, the incremented array Y
must contain the vector y. On exit, Y is overwritten by the
updated vector y.
```

*INCY*

```
INCY is INTEGER
On entry, INCY specifies the increment for the elements of
Y. INCY must not be zero.
Unchanged on exit.
```

**Author:**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

**Date:**

September 2012

**Further Details:**

```
Level 2 Blas routine.
-- Written on 22-October-1986.
Jack Dongarra, Argonne National Lab.
Jeremy Du Croz, Nag Central Office.
Sven Hammarling, Nag Central Office.
Richard Hanson, Sandia National Labs.
-- Modified for the absolute-value product, April 2006
Jason Riedy, UC Berkeley
```

Definition at line 177 of file sla_syamv.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

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

Sat Nov 16 2013 Version 3.4.2 LAPACK