# naginterfaces.library.blas.dtbmv¶

naginterfaces.library.blas.dtbmv(uplo, trans, diag, k, a, x)[source]

dtbmv computes the matrix-vector product for a real triangular band matrix or its transpose.

For full information please refer to the NAG Library document for f06pg

https://www.nag.com/numeric/nl/nagdoc_28.7/flhtml/f06/f06pgf.html

Parameters
uplostr, length 1

Specifies whether is upper or lower triangular.

is upper triangular.

is lower triangular.

transstr, length 1

Specifies the operation to be performed.

.

or

.

diagstr, length 1

Specifies whether has nonunit or unit diagonal elements.

The diagonal elements are stored explicitly.

The diagonal elements are assumed to be , and are not referenced.

kint

, the number of subdiagonals or superdiagonals of the matrix .

afloat, array-like, shape

The triangular band matrix

xfloat, array-like, shape

The -element vector .

Returns
xfloat, ndarray, shape

The updated vector .

Raises
NagValueError
(errno )

On entry, error in parameter .

Constraint: or .

(errno )

On entry, error in parameter .

Constraint: , or .

(errno )

On entry, error in parameter .

Constraint: or .

(errno )

On entry, error in parameter .

Constraint: .

(errno )

On entry, error in parameter .

Constraint: .

(errno )

On entry, error in parameter .

Constraint: .

Notes

In the NAG Library the traditional C interface for this routine uses a different algorithmic base. Please contact NAG if you have any questions about compatibility.

dtbmv performs one of the matrix-vector operations

where is an real triangular band matrix with subdiagonals or superdiagonals, and is an -element real vector.