?spr

Developer Reference for Intel® oneAPI Math Kernel Library for C

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ID 766684

Date 4/28/2026

Version

Public

?spr

Performs a rank-1 update of a symmetric packed matrix.

Syntax

void cblas_sspr(const CBLAS_LAYOUT Layout, const CBLAS_UPLO uplo, const MKL_INT n,
                const float alpha, const float *x, const MKL_INT incx, float *ap);

void cblas_dspr(const CBLAS_LAYOUT Layout, const CBLAS_UPLO uplo, const MKL_INT n,
                const double alpha, const double *x, const MKL_INT incx, double *ap);

Include Files

mkl.h

Description

The ?spr routines perform a matrix-vector operation defined as a := alpha * x * x ‘+ A ,

where:

alpha is a real scalar,

x is an n -element vector,

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

Specifies whether the upper or lower triangular part of the matrix A is supplied in the packed array ap .

If uplo = CblasUpper , then the upper triangular part of the matrix A is supplied in the packed array ap .

If uplo = CblasLower , then the low triangular part of the matrix A is supplied in the packed array ap .

n

Specifies the order of the matrix A . The value of n must be at least zero.

alpha: REAL for sspr DOUBLE PRECISION for dspr Specifies the scalar alpha .
x: REAL for sspr DOUBLE PRECISION for dspr Array, size at least (1 + (n - 1)*abs(incx)) . Before entry, the incremented array x must contain the n -element vector x .

incx

Specifies the increment for the elements of x .

The value of incx must not be zero.

ap

REAL for sspr DOUBLE PRECISION for dspr For Layout = CblasColMajor :

Before entry with uplo = CblasUpper , the array ap must contain the upper triangular part of the symmetric matrix packed sequentially, column-by-column, so that ap(1)ap[0] contains A_{1, 1} , ap(2)ap[1] and ap(3)ap[2] contain A_{1, 2} and A_{2, 2} respectively, and so on.

Before entry with uplo = CblasLower , the array ap must contain the lower triangular part of the symmetric matrix packed sequentially, column-by-column, so that ap(1)ap[0] contains A_{1, 1} , ap(2)ap[1] and ap(3)ap[2] 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 A_{1, 1} , ap[1] and ap[2] contain A_{1, 2} and A_{1, 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 A_{1, 1} , ap[1] and ap[2] contain A_{2, 1} and A_{2, 2} respectively, and so on.

Output Parameters

ap

With uplo = CblasUpper , overwritten by the upper triangular part of the updated matrix.

With uplo = CblasLower , overwritten by the lower triangular part of the updated matrix.

BLAS 95 Interface Notes

There exist FORTRAN 77 and FORTRAN 95 interfaces for this routine. See the Intel® oneMKL Fortran Developer Reference for details.

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Developer Reference for Intel® oneAPI Math Kernel Library for C

?spr

Syntax

Include Files

Description

Input Parameters

Output Parameters

BLAS 95 Interface Notes