?gemv

Developer Reference for Intel® oneAPI Math Kernel Library for Fortran

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ID 766686

Date 12/16/2022

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?gemv

Computes a matrix-vector product using a general matrix.

Syntax

call sgemv(trans, m, n, alpha, a, lda, x, incx, beta, y, incy)

call dgemv(trans, m, n, alpha, a, lda, x, incx, beta, y, incy)

call cgemv(trans, m, n, alpha, a, lda, x, incx, beta, y, incy)

call zgemv(trans, m, n, alpha, a, lda, x, incx, beta, y, incy)

call scgemv(trans, m, n, alpha, a, lda, x, incx, beta, y, incy)

call dzgemv(trans, m, n, alpha, a, lda, x, incx, beta, y, incy)

call gemv(a, x, y [,alpha][,beta] [,trans])

Include Files

mkl.fi, blas.f90

Description

The ?gemv routines perform a matrix-vector operation defined as:

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

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

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

where:

alpha and beta are scalars,

x and y are vectors,

A is an m-by-n matrix.

Input Parameters

trans

CHARACTER*1 Specifies the operation:

if trans= 'N' or 'n', then y := alpha*A*x + beta*y;

if trans= 'T' or 't', then y := alpha*A'*x + beta*y;

if trans= 'C' or 'c', then y := alpha *conjg(A')*x + beta*y.

m

INTEGER. Specifies the number of rows of the matrix A. The value of m must be at least zero.

n

INTEGER. Specifies the number of columns of the matrix A. The value of n must be at least zero.

alpha

REAL for sgemv

DOUBLE PRECISION for dgemv

COMPLEX for cgemv, scgemv

DOUBLE COMPLEX for zgemv, dzgemv

Specifies the scalar alpha.

a

REAL for sgemv, scgemv

DOUBLE PRECISION for dgemv, dzgemv

COMPLEX for cgemv

DOUBLE COMPLEX for zgemv

Array, size (lda, n).

Before entry, the leading m-by-n part of the array a must contain the matrix of coefficients.

lda

INTEGER. Specifies the leading dimension of a as declared in the calling (sub)program.

The value of lda must be at least max(1, m).

x

REAL for sgemv

DOUBLE PRECISION for dgemv

COMPLEX for cgemv, scgemv

DOUBLE COMPLEX for zgemv, dzgemv

Array, size 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.

incx

INTEGER. Specifies the increment for the elements of x.

The value of incx must not be zero.

beta

REAL for sgemv

DOUBLE PRECISION for dgemv

COMPLEX for cgemv, scgemv

DOUBLE COMPLEX for zgemv, dzgemv

Specifies the scalar beta. When beta is set to zero, then y need not be set on input.

y

REAL for sgemv

DOUBLE PRECISION for dgemv

COMPLEX for cgemv, scgemv

DOUBLE COMPLEX for zgemv, dzgemv

Array, size at least (1 +(m - 1)*abs(incy)) when trans= 'N' or 'n' and at least (1 +(n - 1)*abs(incy)) otherwise. Before entry with non-zero beta, the incremented array y must contain the vector y.

incy

INTEGER. Specifies the increment for the elements of y.

The value of incy must not be zero.

Output Parameters

y: Updated vector y.

BLAS 95 Interface Notes

Routines in Fortran 95 interface have fewer arguments in the calling sequence than their FORTRAN 77 counterparts. For general conventions applied to skip redundant or reconstructible arguments, see BLAS 95 Interface Conventions.

Specific details for the routine gemv interface are the following:

a

Holds the matrix A of size (m,n).

x

Holds the vector with the number of elements rx where rx = n if trans = 'N', rx = m otherwise.

y

Holds the vector with the number of elements ry where ry = m if trans = 'N', ry = n otherwise.

trans

Must be 'N', 'C', or 'T'.

The default value is 'N'.

alpha

The default value is 1.

beta

The default value is 0.

Parent topic: BLAS Level 2 Routines

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?gemv