Re: [ublas] [BLAS bindings] help appreciated on using trmv and gbmv

Subject: Re: [ublas] [BLAS bindings] help appreciated on using trmv and gbmv
From: Florent Teichteil (florent.teichteil_at_[hidden])
Date: 2012-10-08 03:24:28

Le 08/10/2012 08:54, Rutger ter Borg a écrit :
> On 2012-10-07 22:50, Florent Teichteil wrote:
>> For those trying to compile my tests, I forgot to remove line 12 in
>> file test.cc. I'm reattaching it.
>>
>
> Hello Florent,
>
> my first remark is that blas (and lapack) routines are data_storage
> dependent. In other words, the routines assume things on how to iterate
> over the data. So, if a routine works with a dense storage layout, like
> trmv, it will not work with a packed storage layout.
>
> That said, I think there are blas-routines for some blas-unsupported
> packed storage structures available somewhere in lapack, but we don't
> have bindings for those yet. If you want efficient computations, go with
> non-packed storage.
>
> I will check, but I think the above will hold true for most of your
> "DOES NOT COMPILE" statements. It shouldn't compile.
>

Ok, it makes totally sense. Actually, I was confused by wikipedia, which 
indicates that blas supports packed storage matrix: 
http://en.wikipedia.org/wiki/Packed_storage_matrix
It was unclear that this storage layout was only available through lapack.

That said, most of my tests concern triangular or banded views of 
*dense* matrices, for which I get incorrect results.

Best,
Florent