On 2012-10-08 14:33, Florent Teichteil wrote:

>

> You're right, computations with trmv are correct with values of

> reasonable magnitudes, let say between -500 and 500 for instance.

> Actually, I figured out why it didn't work with very large values
up to

> RAND_MAX: depending on the computations performed by gemv or trmv,
some

> temporary values exceeded the maximum value that can be represented
by a

> double number (for instance, RAND_MAX * RAND_MAX can not be represented

> using double precision numbers).

>

> That said... The bindings for banded matrices, i.e. gbmv, still give

> incorrect results with matrices and vectors filled with reasonable

> values. Moreover, the only transpose operator that makes sense

> (according to your previous post), does not compile with

> banded_adaptors. So:

>

> 1. How can I get correct results with gbmv (even with matrices and

> vectors filled with the same value of 1.0)?

>

> 2. How can I transpose a banded-adapted matrix before calling gbmv,

> using boost::numeric::bindings::trans?

>

> Cheers,

> Florent

>

Hello Florent,

1) you don't clear the banded matrix B, in my case M != B. If you do 

that, the routines using the packed banded storage start to work. 

blas::gbmv assumes packed storage.

2) The banded adaptor of the dense matrix doesn't work with blas::gbmv

because the memory model isn't compatible. Maybe we can apply a trick to

the memory model, such as passing a* = begin_value(A)-kl and lda += 1?

We would need to check that. Until then, it is not supported.

Regards,

Rutger

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