?her2

Developer Reference for Intel® oneAPI Math Kernel Library for C

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ID 766684

Date 10/15/2026

Version

Public

?her2

Performs a rank-2 update of a Hermitian matrix.

Syntax

void cblas_cher2(const CBLAS_LAYOUT Layout, const CBLAS_UPLO uplo, const MKL_INT n,
                 const void *alpha, const void *x, const MKL_INT incx, const void *y,
                 const MKL_INT incy, void *a, const MKL_INT lda);

void cblas_zher2(const CBLAS_LAYOUT Layout, const CBLAS_UPLO uplo, const MKL_INT n,
                 const void *alpha, const void *x, const MKL_INT incx, const void *y,
                 const MKL_INT incy, void *a, const MKL_INT lda);

Include Files

mkl.h

Description

The ?her2 routines perform a matrix-vector operation defined as A := alpha *x*conjg( y' ) + conjg( alpha )* y *conjg( x' ) + A ,

where:

alpha is scalar,

x and y are n -element vectors,

A is an n -by- n Hermitian 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 of the array a is used.

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

n

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

alpha

COMPLEX for cher2 DOUBLE COMPLEX for zher2 Specifies the scalar alpha .

x

COMPLEX for cher2 DOUBLE COMPLEX for zher2 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

COMPLEX for cher2 DOUBLE COMPLEX for zher2 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

COMPLEX for cher2 DOUBLE COMPLEX for zher2 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 Hermitian 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 Hermitian matrix and the strictly upper triangular part of a is not referenced.

The imaginary parts of the diagonal elements need not be set and are assumed to be zero.

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.

If alpha is zero, matrix A is unchanged; otherwise, the imaginary parts of the diagonal elements are set to zero.

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

?her2

Syntax

Include Files

Description

Input Parameters

Output Parameters

BLAS 95 Interface Notes