# naginterfaces.library.lapackeig.dsytrd¶

naginterfaces.library.lapackeig.dsytrd(uplo, a)[source]

dsytrd reduces a real symmetric matrix to tridiagonal form.

For full information please refer to the NAG Library document for f08fe

https://www.nag.com/numeric/nl/nagdoc_28.7/flhtml/f08/f08fef.html

Parameters
uplostr, length 1

Indicates whether the upper or lower triangular part of is stored.

The upper triangular part of is stored.

The lower triangular part of is stored.

afloat, array-like, shape

The symmetric matrix .

Returns
afloat, ndarray, shape

is overwritten by the tridiagonal matrix and details of the orthogonal matrix as specified by .

dfloat, ndarray, shape

The diagonal elements of the tridiagonal matrix .

efloat, ndarray, shape

The off-diagonal elements of the tridiagonal matrix .

taufloat, ndarray, shape

Further details of the orthogonal matrix .

Raises
NagValueError
(errno )

On entry, error in parameter .

Constraint: or .

(errno )

On entry, error in parameter .

Constraint: .

Notes

dsytrd reduces a real symmetric matrix to symmetric tridiagonal form by an orthogonal similarity transformation: .

The matrix is not formed explicitly but is represented as a product of elementary reflectors (see the F08 Introduction for details). Functions are provided to work with in this representation (see Further Comments).

References

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