Developer Reference for Intel® oneAPI Math Kernel Library for Fortran
?spmv
Computes a matrix-vector product with a symmetric packed matrix.
Syntax
call sspmv(uplo, n, alpha, ap, x, incx, beta, y, incy)
call dspmv(uplo, n, alpha, ap, x, incx, beta, y, incy)call spmv(ap, x, y [, uplo] [, alpha] [, beta])Include Files
mkl.fi, mkl_blas.f90
Description
The ?spmv routines perform a matrix-vector operation defined as y := alpha * A * x + beta * y ,
where:
alpha and beta are scalars,
x and y are n -element vectors,
A is an n -by- n symmetric matrix, supplied in packed form.
Input Parameters
- Layout
-
Specifies whether two-dimensional array storage is row-major ( CblasRowMajor ) or column-major ( CblasColMajor ).
uplo
CHARACTER*1 . Specifies whether the upper or lower triangular part of the matrix A is supplied in the packed array ap .
If uplo = 'U' or ‘u’ uplo = CblasUpper , then the upper triangular part of the matrix A is supplied in the packed array ap .
If uplo = 'L' or ‘l’ , then the low triangular part of the matrix A is supplied in the packed array ap .
n
INTEGER . Specifies the order of the matrix A . The value of n must be at least zero.
- alpha
-
REAL for sspmv DOUBLE PRECISION for dspmv Specifies the scalar alpha .
- ap
-
REAL for sspmv DOUBLE PRECISION for dspmv Array, size at least ((n*(n + 1))/2) . For Layout = CblasColMajor :
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.
For Layout = CblasRowMajor : Before entry with uplo = CblasUpper , the array ap must contain the upper triangular part of the symmetric matrix packed sequentially, row-by-row, ap[0] contains A1, 1 , ap[1] and ap[2] contain A1, 2 and A1, 3 respectively, and so on. Before entry with uplo = CblasLower , the array ap must contain the lower triangular part of the symmetric matrix packed sequentially, row-by-row, so that ap[0] contains A1, 1 , ap[1] and ap[2] contain A2, 1 and A2, 2 respectively, and so on.
- x
-
REAL for sspmv DOUBLE PRECISION for dspmv Array, size at least (1 + (n - 1)*abs(incx)) . Before entry, the incremented array x must contain the n -element vector x .
incx
INTEGER . Specifies the increment for the elements of x .
The value of incx must not be zero.
- beta
-
REAL for sspmv DOUBLE PRECISION for dspmv Specifies the scalar beta . When beta is supplied as zero, then y need not be set on input.
- y
-
REAL for sspmv DOUBLE PRECISION for dspmv Array, size at least (1 + (n - 1)*abs(incy)) . Before entry, the incremented array y must contain the n -element vector y .
incy
INTEGER . Specifies the increment for the elements of y .
The value of incy must not be zero.
Output Parameters
- y
-
Overwritten by the 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 spmv interface are the following:
- ap
-
Holds the array ap of size ( n*(n+1)/2 ).
- x
-
Holds the vector with the number of elements n .
- y
-
Holds the vector with the number of elements n .
- uplo
-
Must be ‘U’ or ‘L’ . The default value is ‘U’ .
- alpha
-
The default value is 1.
- beta
-
The default value is 0.