# naginterfaces.library.lapacklin.dsysv¶

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

dsysv computes the solution to a real system of linear equations

where is an symmetric matrix and and are matrices.

For full information please refer to the NAG Library document for f07ma

https://www.nag.com/numeric/nl/nagdoc_27.3/flhtml/f07/f07maf.html

Parameters
uplostr, length 1

If , the upper triangle of is stored.

If , the lower triangle of is stored.

afloat, array-like, shape

The symmetric matrix .

bfloat, array-like, shape

The right-hand side matrix .

Returns
afloat, ndarray, shape

If no exception or warning is raised, the block diagonal matrix and the multipliers used to obtain the factor or from the factorization or as computed by dsytrf().

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.

bfloat, ndarray, shape

If no exception or warning is raised, the solution matrix .

Raises
NagValueError
(errno )

On entry, error in parameter .

Constraint: or .

(errno )

On entry, error in parameter .

Constraint: .

(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, so the solution could not be computed.

Notes

dsysv uses the diagonal pivoting method to factor as if or if , where (or ) is a product of permutation and unit upper (lower) triangular matrices, and is symmetric and block diagonal with and diagonal blocks. The factored form of is then used to solve the system of equations .

Note that, in general, different permutations (pivot sequences) and diagonal block structures are obtained for or

References

Anderson, E, Bai, Z, Bischof, C, Blackford, S, Demmel, J, Dongarra, J J, Du Croz, J J, Greenbaum, A, Hammarling, S, McKenney, A and Sorensen, D, 1999, LAPACK Users’ Guide, (3rd Edition), SIAM, Philadelphia, https://www.netlib.org/lapack/lug

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