?lagsy

Developer Reference for Intel® oneAPI Math Kernel Library for C

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ID 766684

Date 10/15/2026

Version

Public

?lagsy

Generates a symmetric matrix by pre- and post- multiplying a real diagonal matrix with a random unitary matrix .

Syntax

lapack_int LAPACKE_slagsy(int matrix_layout, lapack_int n, lapack_int k, const float *d,
                          float *a, lapack_int lda, lapack_int *iseed);

lapack_int LAPACKE_dlagsy(int matrix_layout, lapack_int n, lapack_int k, const double *d,
                          double *a, lapack_int lda, lapack_int *iseed);

lapack_int LAPACKE_clagsy(int matrix_layout, lapack_int n, lapack_int k, const float *d,
                          lapack_complex_float *a, lapack_int lda, lapack_int *iseed);

lapack_int LAPACKE_zlagsy(int matrix_layout, lapack_int n, lapack_int k, const double *d,
                          lapack_complex_double *a, lapack_int lda, lapack_int *iseed);

Include Files

mkl.h

Description

The ?lagsy routine generates a symmetric matrix A by pre- and post- multiplying a real diagonal matrix D with a random matrix U :

A := U*D*U^{T} ,

where U is orthogonal for real flavors and unitary for complex flavors. The semi-bandwidth may then be reduced to k by additional unitary transformations.

Input Parameters

A <datatype> placeholder, if present, is used for the C interface data types in the C interface section above. See C Interface Conventions for the C interface principal conventions and type definitions.

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

k

The number of nonzero subdiagonals within the band of A ( 0 ≤k≤n-1) .

d: REAL for slagsy , clagsy DOUBLE PRECISION for dlagsy , zlagsy . The array d with the dimension of ( n ) contains the diagonal elements of the diagonal matrix D .

lda

The leading dimension of the array a ( lda≥n ).

iseed

The array iseed with the dimension of 4 contains the seed of the random number generator. The elements must be between 0 and 4095 and iseed(4)[3] must be odd.

Output Parameters

a

REAL for slagsy DOUBLE PRECISION for dlagsy COMPLEX for clagsy DOUBLE COMPLEX for zlagsy .

The array a of size max (1, lda * n ) contains the generated symmetric n -by- n matrix D .

iseed

The array iseed contains the updated seed on exit.

Return Values

This function returns a value info .

If info = 0 , the execution is successful.
If info < 0 , the i -th parameter had an illegal value.
If info = -1011 , memory allocation error occurred.

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Developer Reference for Intel® oneAPI Math Kernel Library for C

?lagsy

Syntax

Include Files

Description

Input Parameters

Output Parameters

Return Values