sspmv.f −

**Functions/Subroutines**

subroutine **sspmv** (UPLO, N, ALPHA, AP, X, INCX, BETA, Y, INCY)

SSPMV

**subroutine sspmv (characterUPLO, integerN, realALPHA, real, dimension(*)AP, real, dimension(*)X, integerINCX, realBETA, real, dimension(*)Y, integerINCY)
SSPMV Purpose:**

SSPMV performs the matrix-vector operation

y := alpha*A*x + beta*y,

where alpha and beta are scalars, x and y are n element vectors and

A is an n by n symmetric matrix, supplied in packed form.

**Parameters:**

*UPLO*

UPLO is CHARACTER*1

On entry, UPLO specifies whether the upper or lower

triangular part of the matrix A is supplied in the packed

array AP as follows:

UPLO = ’U’ or ’u’ The upper triangular part of A is

supplied in AP.

UPLO = ’L’ or ’l’ The lower triangular part of A is

supplied in AP.

*N*

N is INTEGER

On entry, N specifies the order of the matrix A.

N must be at least zero.

*ALPHA*

ALPHA is REAL

On entry, ALPHA specifies the scalar alpha.

*AP*

AP is REAL array of DIMENSION at least

( ( n*( n + 1 ) )/2 ).

Before entry with UPLO = ’U’ or ’u’, the array AP must

contain the upper triangular part of the symmetric matrix

packed sequentially, column by column, so that AP( 1 )

contains a( 1, 1 ), AP( 2 ) and AP( 3 ) contain a( 1, 2 )

and a( 2, 2 ) respectively, and so on.

Before entry with UPLO = ’L’ or ’l’, the array AP must

contain the lower triangular part of the symmetric matrix

packed sequentially, column by column, so that AP( 1 )

contains a( 1, 1 ), AP( 2 ) and AP( 3 ) contain a( 2, 1 )

and a( 3, 1 ) respectively, and so on.

*X*

X is REAL array of dimension at least

( 1 + ( n - 1 )*abs( INCX ) ).

Before entry, the incremented array X must contain the n

element vector x.

*INCX*

INCX is INTEGER

On entry, INCX specifies the increment for the elements of

X. INCX must not be zero.

*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.

*Y*

Y is REAL array of dimension at least

( 1 + ( n - 1 )*abs( INCY ) ).

Before entry, the incremented array Y must contain the n

element 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.

**Author:**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

**Date:**

November 2011

**Further Details:**

Level 2 Blas routine.

The vector and matrix arguments are not referenced when N = 0, or M = 0

-- 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.

Definition at line 148 of file sspmv.f.

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