Re: [Help-gsl] Vector-Matrix Multiplication

[Michael Lehn]

Am 30.10.2012 um 14:35 schrieb Dimitris K.:

> For clarification, since I can't find anything in the docs, I want to ask.
> 
> Say I want to compute the following:
> 
> y = \alpha x op(A) + \beta y (where x,y are vectors and A is a matrix),
> 

So if op(A)=A your vectors are row-rectors.  In this case the operation is
equivalent to

 y = \alpha A^T  x + \beta y

where x and y are column-vectors.  Other cases of op(A) can be treated
analogously.  

As BLAS does not distinguish between col- and row-vectors you just can
use gemv.

If elements are complex valued there is a problem though.  Officially
gemv in BLAS does not support an operation like

 y = \alpha conj(A)  x + \beta y

which would be required in your case if op(A)=A^H.  However, (I think)
some BLAS implementation actually support it (TRANSA='R').

Cheers,

Michael