?syr2

Developer Reference for Intel® oneAPI Math Kernel Library for C

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ID 766684

Date 4/28/2026

Version

Public

?syr2

Performs a rank-2 update of a symmetric matrix.

Syntax

void cblas_ssyr2(const CBLAS_LAYOUT Layout, const CBLAS_UPLO uplo, const MKL_INT n,
                 const float alpha, const float *x, const MKL_INT incx, const float *y,
                 const MKL_INT incy, float *a, const MKL_INT lda);

void cblas_dsyr2(const CBLAS_LAYOUT Layout, const CBLAS_UPLO uplo, const MKL_INT n,
                 const double alpha, const double *x, const MKL_INT incx, const double *y,
                 const MKL_INT incy, double *a, const MKL_INT lda);

Include Files

mkl.h

Description

The ?syr2 routines perform a matrix-vector operation defined as A := alpha * x * y ‘+ alpha * y * x ‘ + A ,

where:

alpha is scalar,

x and y are n -element vectors,

A is an n -by- n symmetric matrix.

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 array a is used.

If uplo = CblasUpper , then the upper triangular part of the array a is used.

If uplo = CblasLower , then the low triangular part of the array a is used.

n

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

alpha: REAL for ssyr2 DOUBLE PRECISION for dsyr2 Specifies the scalar alpha .
x: REAL for ssyr2 DOUBLE PRECISION for dsyr2 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.

y: REAL for ssyr2 DOUBLE PRECISION for dsyr2 Array, size at least (1 + (n - 1)*abs(incy)) . Before entry, the incremented array y must contain the n -element vector y .

incy

Specifies the increment for the elements of y . The value of incy must not be zero.

a

REAL for ssyr2 DOUBLE PRECISION for dsyr2 Array, size (lda, n)lda*n .

Before entry with uplo = CblasUpper , the leading n -by- n upper triangular part of the array a must contain the upper triangular part of the symmetric matrix and the strictly lower triangular part of a is not referenced.

Before entry with uplo = CblasLower , the leading n -by- n lower triangular part of the array a must contain the lower triangular part of the symmetric matrix and the strictly upper triangular part of a is not referenced.

lda

Specifies the leading dimension of a as declared in the calling (sub)program. The value of lda must be at least max(1, n) .

Output Parameters

a

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

With uplo = CblasLower , the lower triangular part of the array a is 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

?syr2

Syntax

Include Files

Description

Input Parameters

Output Parameters

BLAS 95 Interface Notes