# naginterfaces.library.lapacklin.zsytrf¶

naginterfaces.library.lapacklin.zsytrf(uplo, a)[source]

zsytrf computes the Bunch–Kaufman factorization of a complex symmetric matrix.

For full information please refer to the NAG Library document for f07nr

https://www.nag.com/numeric/nl/nagdoc_27.3/flhtml/f07/f07nrf.html

Parameters
uplostr, length 1

Specifies whether the upper or lower triangular part of is stored and how is to be factorized.

The upper triangular part of is stored and is factorized as , where is upper triangular.

The lower triangular part of is stored and is factorized as , where is lower triangular.

acomplex, array-like, shape

The symmetric indefinite matrix .

Returns
acomplex, ndarray, shape

The upper or lower triangle of is overwritten by details of the block diagonal matrix and the multipliers used to obtain the factor or as specified by .

ipivint, ndarray, shape

Details of the interchanges and the block structure of . More precisely,

if , is a pivot block and the th row and column of were interchanged with the th row and column;

if and , is a pivot block and the th row and column of were interchanged with the th row and column;

if and , is a pivot block and the th row and column of were interchanged with the th row and column.

Raises
NagValueError
(errno )

On entry, error in parameter .

Constraint: or .

(errno )

On entry, error in parameter .

Constraint: .

Warns
NagAlgorithmicWarning
(errno )

Element of the diagonal is exactly zero. The factorization has been completed, but the block diagonal matrix is exactly singular, and division by zero will occur if it is used to solve a system of equations.

Notes

zsytrf factorizes a complex symmetric matrix , using the Bunch–Kaufman diagonal pivoting method. is factorized as either if or if , where is a permutation matrix, (or ) is a unit upper (or lower) triangular matrix and is a symmetric block diagonal matrix with and diagonal blocks; (or ) has unit diagonal blocks corresponding to the blocks of . Row and column interchanges are performed to ensure numerical stability while preserving symmetry.

References

Golub, G H and Van Loan, C F, 1996, Matrix Computations, (3rd Edition), Johns Hopkins University Press, Baltimore