# naginterfaces.library.blas.dgbmv¶

naginterfaces.library.blas.dgbmv(trans, m, kl, ku, alpha, a, x, beta, y=None)[source]

dgbmv computes the matrix-vector product for a real general band matrix or its transpose.

For full information please refer to the NAG Library document for f06pb

https://www.nag.com/numeric/nl/nagdoc_28.5/flhtml/f06/f06pbf.html

Parameters
transstr, length 1

Specifies the operation to be performed.

.

or

.

mint

, the number of rows of the matrix .

klint

, the number of subdiagonals within the band of .

kuint

, the number of superdiagonals within the band of .

alphafloat

The scalar .

afloat, array-like, shape

The band matrix .

xfloat, array-like, shape

Note: the required length for this argument is determined as follows: if : ; if : ; otherwise: .

The vector .

betafloat

The scalar .

yNone or float, array-like, shape , optional

Note: the required length for this argument is determined as follows: if : ; if : ; otherwise: .

The vector , if , need not be set.

Returns
yfloat, ndarray, shape

The updated vector .

Raises
NagValueError
(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: .

(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.

dgbmv performs one of the matrix-vector operations

where is an real band matrix with subdiagonals and superdiagonals, and are real vectors, and and are real scalars.

If or , no operation is performed.