# HPL_dgemv man page

HPL_dgemv — y := beta * y + alpha * op(A) * x.

## Synopsis

**#include "hpl.h"****void HPL_dgemv( const enum HPL_ORDER** *ORDER*, **const enum HPL_TRANS** *TRANS*, **const int** *M*, **const int** *N*, **const double** *ALPHA*, **const double *** *A*, **const int** *LDA*, **const double *** *X*, **const int** *INCX*, **const double** *BETA*, **double *** *Y*, **const int** *INCY* **);**

## Description

**HPL_dgemv** performs one of the matrix-vector operations

y := alpha * op( A ) * x + beta * y,

where op( X ) is one of

op( X ) = X or op( X ) = X^T.

where alpha and beta are scalars, x and y are vectors and A is an m by n matrix.

## Arguments

- ORDER (local input) const enum HPL_ORDER
- On entry, ORDER specifies the storage format of the operands as follows:

ORDER = HplRowMajor,

ORDER = HplColumnMajor. - TRANS (local input) const enum HPL_TRANS
- On entry, TRANS specifies the operation to be performed as follows:

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

TRANS = HplTrans y := alpha*A^T*x + beta*y. - M (local input) const int
- On entry, M specifies the number of rows of the matrix A. M must be at least zero.
- N (local input) const int
- On entry, N specifies the number of columns of the matrix A. N must be at least zero.
- ALPHA (local input) const double
- On entry, ALPHA specifies the scalar alpha. When ALPHA is supplied as zero then A and X need not be set on input.
- A (local input) const double *
- On entry, A points to an array of size equal to or greater than LDA * n. Before entry, the leading m by n part of the array A must contain the matrix coefficients.
- LDA (local input) const int
- On entry, LDA specifies the leading dimension of A as declared in the calling (sub) program. LDA must be at least MAX(1,m).
- X (local input) const double *
- On entry, X is an incremented array of dimension at least ( 1 + ( n - 1 ) * abs( INCX ) ) that contains the vector x.
- INCX (local input) const int
- On entry, INCX specifies the increment for the elements of X. INCX must not be zero.
- BETA (local input) const double
- On entry, BETA specifies the scalar beta. When ALPHA is supplied as zero then Y need not be set on input.
- Y (local input/output) double *
- On entry, Y is an incremented array of dimension at least ( 1 + ( n - 1 ) * abs( INCY ) ) that contains the vector y. 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 (local input) const int
- On entry, INCY specifies the increment for the elements of Y. INCY must not be zero.

## Example

*#include "hpl.h"*

int main(int argc, char *argv[])

{

double a[2*2], x[2], y[2];

a[0] = 1.0; a[1] = 2.0; a[2] = 3.0; a[3] = 3.0;

x[0] = 2.0; x[1] = 1.0; y[2] = 1.0; y[3] = 2.0;

HPL_dgemv( HplColumnMajor, HplNoTrans, 2, 2, 2.0,

a, 2, x, 1, -1.0, y, 1 );

printf("y=[%f,%f]\n", y[0], y[1]);

exit(0); return(0);

}

## See Also

**HPL_dger** (3), **HPL_dtrsv** (3).