Developer Reference for Intel® oneAPI Math Kernel Library for Fortran
?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, mkl_blas.f90
Description
The ?gemv routines perform a matrix-vector operation defined as:
y := alpha*A*x + beta*y ,
or
y := alpha*A'*x + beta*y ,
or
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
- Layout
-
Specifies whether two-dimensional array storage is row-major ( CblasRowMajor ) or column-major ( CblasColMajor ).
- trans
-
Specifies the operation: if trans = CblasNoTrans , then y := alpha*A*x + beta*y ; if trans = CblasTrans , then y := alpha*A'*x + beta*y ; if trans = CblasConjTrans , then y := alpha *conjg(A')*x + beta*y . 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. Array, size lda * k . For Layout = CblasColMajor , k is n . Before entry, the leading m -by- n part of the array a must contain the matrix A . For Layout = CblasRowMajor , k is m . Before entry, the leading n -by- m part of the array a must contain the matrix A .
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) . For Layout = CblasColMajor , the value of lda must be at least max(1, m) . For Layout = CblasRowMajor , the value of lda must be at least max(1, n) .
- 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 = CblasNoTrans and at least (1+(m - 1)*abs(incx)) otherwise. Before entry, the incremented array x must contain the vector x . 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 = CblasNoTrans and at least (1 +(n - 1)*abs(incy)) otherwise. Before entry with non-zero beta , the incremented array y must contain the vector y . 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.