?sytrs2

Developer Reference for Intel® oneAPI Math Kernel Library for C

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ID 766684

Date 4/28/2026

Version

Public

?sytrs2

Solves a system of linear equations with a UDU- or LDL-factored symmetric coefficient matrix.

Syntax

lapack_intLAPACKE_ssytrs2 ( intmatrix_layout , charuplo , lapack_intn , lapack_intnrhs , constfloat*a , lapack_intlda , constlapack_int*ipiv , float*b , lapack_intldb );

lapack_intLAPACKE_dsytrs2 ( intmatrix_layout , charuplo , lapack_intn , lapack_intnrhs , constdouble*a , lapack_intlda , constlapack_int*ipiv , double*b , lapack_intldb );

lapack_intLAPACKE_csytrs2 ( intmatrix_layout , charuplo , lapack_intn , lapack_intnrhs , constlapack_complex_float*a , lapack_intlda , constlapack_int*ipiv , lapack_complex_float*b , lapack_intldb );

lapack_intLAPACKE_zsytrs2 ( intmatrix_layout , charuplo , lapack_intn , lapack_intnrhs , constlapack_complex_double*a , lapack_intlda , constlapack_int*ipiv , lapack_complex_double*b , lapack_intldb );

Include Files

mkl.h

Description

The routine solves a system of linear equations A*X = B with a symmetric matrix A using the factorization of A :

if uplo='U' ,

A = U*D*U^{T}

if uplo='L' ,

A = L*D*L^{T}

where

U and L are upper and lower triangular matrices with unit diagonal
D is a symmetric block-diagonal matrix.

The factorization is computed by ?sytrf .

Input Parameters

matrix_layout

Specifies whether matrix storage layout is row major ( LAPACK_ROW_MAJOR ) or column major ( LAPACK_COL_MAJOR ).

uplo

Must be ‘U’ or ‘L’ .

Indicates how the input matrix A has been factored:

If uplo = 'U' , the array a stores the upper triangular factor U of the factorization A = U*D*U^{T} .

If uplo = 'L' , the array a stores the lower triangular factor L of the factorization A = L*D*L^{T} .

n

The order of matrix A ; n ≥ 0.

nrhs

The number of right-hand sides; nrhs ≥ 0.

a , b

The array a of size max(1, lda * n ) contains the block diagonal matrix D and the multipliers used to obtain the factor U or L as computed by ?sytrf .

b

The array b contains the right-hand side matrix B .

The size of b is at least max(1, ldb * nrhs ) for column major layout and max(1, ldb * n ) for row major layout.

lda

The leading dimension of a ; lda≥ max(1, n) .

ldb

The leading dimension of b ; ldb≥ max(1, n)ldb ≥ max(1, n ) for column major layout and ldb ≥ nrhs for row major layout .

ipiv

Array of size n . The ipiv array contains details of the interchanges and the block structure of D as determined by ?sytrf .

work

Workspace array, size n .

Output Parameters

b

Overwritten by the solution matrix X .

Return Values

This function returns a value info .

If info = 0 , the execution is successful.
If info = -i , parameter i had an illegal value.

LAPACK 95 Interface Notes

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

NOTE:

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Developer Reference for Intel® oneAPI Math Kernel Library for C

?sytrs2

Syntax

Include Files

Description

Input Parameters

Output Parameters

Return Values

LAPACK 95 Interface Notes