Computes the solution to system of linear equations for HE matrices.

LAPACK_DECL lapack_int LAPACKE_chesv_aa (int matrix_layout, char uplo, lapack_int n, lapack_int nrhs, lapack_complex_float * a, lapack_int lda, lapack_int * ipiv, lapack_complex_float * b, lapack_int ldb );

LAPACK_DECL lapack_int LAPACKE_chesv_aa_work (int matrix_layout, char uplo, lapack_int n, lapack_int nrhs, lapack_complex_float * a, lapack_int lda, lapack_int * ipiv, lapack_complex_float * b, lapack_int ldb, lapack_complex_float * work, lapack_int lwork );

## Description

?hesv_aa computes the solution to a complex system of linear equations A * X = B, where A is an n-by-n Hermitian matrix and X and B are n-by-nrhs matrices. Aasen's algorithm is used to factor A as

A = U * T * UH if uplo = 'U', or

A = L * T * LH if uplo = 'L',

where U (or L) is a product of permutation and unit upper (lower) triangular matrices, and T is Hermitian and tridiagonal. The factored form of A is then used to solve the system of equations A * X = B.

## Input Parameters

matrix_layout

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

uplo

If uplo = 'U': The upper triangle of A is stored.

If uplo = 'L': the lower triangle of A is stored.

n

The number of linear equations or the order of the matrix A. n 0.

nrhs

The number of right hand sides or the number of columns of the matrix B. nrhs 0.

a

Array of size lda*n. On entry, the Hermitian matrix A.

If uplo = 'U', the leading n-by-n upper triangular part of a contains the upper triangular part of the matrix A, and the strictly lower triangular part of a is not referenced.

If uplo = 'L', the leading n-by-n lower triangular part of a contains the lower triangular part of the matrix A, and the strictly upper triangular part of a is not referenced.

lda

The leading dimension of the array a. lda max(1,n).

b

Array of size ldb*nrhs. On entry, the n-by-nrhs right hand side matrix B.

ldb

The leading dimension of the array b. ldb max(1,n).

lwork

The length of work. lwork max(1, 2*n, 3*n-2), and for best performance lwork max(1,n*nb), where nb is the optimal blocksize for ?hetrf.

If lwork < n, TRS is done with Level BLAS 2. If lworkn, TRS is done with Level BLAS 3.

If lwork = -1, then a workspace query is assumed; the routine only calculates the optimal size of the work array, returns this value as the first entry of the work array, and no error message related to lwork is issued by xerbla.

## Output Parameters

a

On exit, if info = 0, the tridiagonal matrix T and the multipliers used to obtain the factor U or L from the factorization A = U*T*UH or A = L*T*LH as computed by ?hetrf_aa.

ipiv

Array of size (n) On exit, it contains the details of the interchanges: row and column k of A were interchanged with the row and column ipiv[k].

b

On exit, if info = 0, the n-by-nrhs solution matrix X.

work

Array of size (max(1, lwork)). On exit, if info = 0, work[0] returns the optimal lwork.

## Return Values

This function returns a value info.

If info = 0: successful exit.

If info < 0: if info = -i, the i-th argument had an illegal value.

If info > 0: if info = i, Di, i is exactly zero. The factorization has been completed, but the block diagonal matrix D is exactly singular, so the solution could not be computed.

For more complete information about compiler optimizations, see our Optimization Notice.