naginterfaces.library.blas.dgemv

naginterfaces.library.blas.dgemv(trans, m, alpha, a, x, beta, y=None)

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

For full information please refer to the NAG Library document for f06pa

https://support.nag.com/numeric/nl/nagdoc_30.3/flhtml/f06/f06paf.html

Parameters

transstr, length 1

Specifies the operation to be performed.

$trans=\text{'N'}$

$y\leftarrow \alpha Ax+\beta y$.

$trans=\text{'T'}$ or $\text{'C'}$

$y\leftarrow \alpha A^{T}x+\beta y$.

mint

$m$, the number of rows of the matrix $A$.

alphafloat

The scalar $\alpha$.

afloat, array-like, shape $(m,n)$

The $m\times n$ matrix $A$.

xfloat, array-like, shape $(:)$

Note: the required length for this argument is determined as follows: if $trans=\text{'N'}$: $n$; if $trans\text{in}(\text{'T'},\text{'C'})$: $m$; otherwise: $0$.

The vector $x$.

betafloat

The scalar $\beta$.

yNone or float, array-like, shape $(:)$, optional

Note: the required length for this argument is determined as follows: if $trans=\text{'N'}$: $m$; if $trans\text{in}(\text{'T'},\text{'C'})$: $n$; otherwise: $0$.

The vector $y$, if $beta=0.0$, $y$ need not be set.

Returns

yfloat, ndarray, shape $(:)$

The updated vector $y$.

Raises

NagValueError

(errno $1$)

On entry, error in parameter $trans$.

Constraint: $trans=\text{'N'}$, $\text{'T'}$ or $\text{'C'}$.

(errno $2$)

On entry, error in parameter $m$.

Constraint: $m\ge 0$.

(errno $3$)

On entry, error in parameter $\text{n}$.

Constraint: $n\ge 0$.

(errno $8$)

On entry, error in parameter $\text{incx}$.

Constraint: $\text{incx}\ne 0$.

(errno $11$)

On entry, error in parameter $\text{incy}$.

Constraint: $\text{incy}\ne 0$.

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.

dgemv performs one of the matrix-vector operations

$$y\leftarrow \alpha Ax+\beta y\text{, or}y\leftarrow \alpha A^{T}x+\beta y\text{,}$$

where $A$ is an $m\times n$ real matrix, $x$ and $y$ are real vectors, and $\alpha$ and $\beta$ are real scalars.

If $m=0$ or $n=0$, no operation is performed.