##### gemv

###### Prototype

There are two prototypes of `gemv` available, please see below.

    gemv( const Scalar >, const MatrixA& a, const VectorX& x,
            const Scalar >, VectorY& y );

    gemv( const Scalar alpha, const MatrixA& a, const VectorX& x,
            const Scalar beta, VectorY& y );

###### Description

`gemv` (short for generic matrix-vector operation) provides a C++ interface to BLAS routines SGEMV, DGEMV, CGEMV, and ZGEMV. `gemv` performs one of the matrix-vector operations

y := alpha*A*x + beta*y, or y := alpha*A'*x + beta*y, or

y := alpha*conjg( A' )*x + beta*y,

where alpha and beta are scalars, x and y are vectors and A is an m by n matrix.

The selection of the BLAS routine is done during compile-time, and is determined by the type of values contained in type `MatrixA`. The type of values is obtained through the `value_type` meta-function `typename value_type<MatrixA>::type`. Table X below illustrates to which specific routine this dispatching will take place.

Table 1.34. Dispatching of gemv.

Value type of MatrixA | BLAS routine | CBLAS routine | CUBLAS routine
--- | --- | --- | ---
`float` | SGEMV | cblas_sgemv | cublasSgemv
`double` | DGEMV | cblas_dgemv | cublasDgemv
`complex<float>` | CGEMV | cblas_cgemv | cublasCgemv
`complex<double>` | ZGEMV | cblas_zgemv | cublasZgemv

The original routines SGEMV, DGEMV, CGEMV, and ZGEMV have eleven arguments, whereas `gemv` requires five arguments.

Table 1.35. Deduction of arguments of gemv.

###### Definition

Defined in header `boost/numeric/bindings/blas/level2/gemv.hpp`.

###### Parameters or Requirements on Types

Parameters

MatrixA

  The definition of term 1

MatrixB

  The definition of term 2

MatrixC

  The definition of term 3.

  Definitions may contain paragraphs.

###### Complexity

###### Example

    #include <boost/numeric/bindings/blas/level2/gemv.hpp>
    using namespace boost::numeric::bindings;

    blas::gemv( x, y, z );

this will output

    [5] 0 1 2 3 4 5

###### Notes

###### See Also

- Originating Fortran source files sgemv.f, dgemv.f, cgemv.f, and zgemv.f at Netlib.