# dgemv

```DGEMV(l)                         BLAS routine                         DGEMV(l)

NAME
DGEMV - perform one of the matrix-vector operations   y := alpha*A*x +
beta*y, or y := alpha*A'*x + beta*y,

SYNOPSIS
SUBROUTINE DGEMV ( TRANS, M, N, ALPHA, A, LDA, X, INCX, BETA, Y, INCY )

DOUBLE       PRECISION ALPHA, BETA

INTEGER      INCX, INCY, LDA, M, N

CHARACTER*1  TRANS

DOUBLE       PRECISION A( LDA, * ), X( * ), Y( * )

PURPOSE
DGEMV  performs one of the matrix-vector operations

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

PARAMETERS
TRANS  - CHARACTER*1.
On entry, TRANS specifies the operation to be performed as
follows:

TRANS = 'N' or 'n'   y := alpha*A*x + beta*y.

TRANS = 'T' or 't'   y := alpha*A'*x + beta*y.

TRANS = 'C' or 'c'   y := alpha*A'*x + beta*y.

Unchanged on exit.

M      - INTEGER.
On entry, M specifies the number of rows of the matrix A.  M
must be at least zero.  Unchanged on exit.

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

ALPHA  - DOUBLE PRECISION.
On entry, ALPHA specifies the scalar alpha.  Unchanged on exit.

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

X      - DOUBLE PRECISION array of DIMENSION at least
( 1 + ( n - 1 )*abs( INCX ) ) when TRANS = 'N' or 'n' and at
least ( 1 + ( m - 1 )*abs( INCX ) ) otherwise.  Before entry,
the incremented array X must contain the vector x.  Unchanged on
exit.

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

BETA   - DOUBLE PRECISION.
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      - DOUBLE PRECISION array of DIMENSION at least
( 1 + ( m - 1 )*abs( INCY ) ) when TRANS = 'N' or 'n' and at
least ( 1 + ( n - 1 )*abs( INCY ) ) otherwise.  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   - INTEGER.
On entry, INCY specifies the increment for the elements of Y.
INCY must not be zero.  Unchanged on exit.

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.

BLAS routine                    16 October 1992                       DGEMV(l)```