about KSP based on parallel dense matrix

[Matthew Knepley]

On Mon, Sep 22, 2008 at 9:43 PM, Lisandro Dalcin <dalcinl at gmail.com> wrote:
> On Mon, Sep 22, 2008 at 11:03 PM, Yujie <recrusader at gmail.com> wrote:
>> Dear Lisandro:
>>
>> Barry has tried to establish an interface for Plapack. However, there are
>> some bugs in Plapack. Therefore, it doesn't work.
>
> Sorry, I didn't know about those Plapack issues.

Neither did I, and seeing as how I use it, this is interesting. Please
please please
report any bugs you find, because I have been using it without problems.

   Matt

>> I am wondering if CG in
>> Petsc can work with parallel dense matrix.
>
> Of course it works. In fact, any other KSP should work. As Barry said,
> The KSP methods are INDEPENDENT of the matrix format, try -pc_type
> jacobi as preconditioner.
>
>> When using the same matrix, which
>> one is faster, sequential or parallel? thanks.
>
> For a fixed-size matrix, you should get really good speedups iterating
> in parallel. Of course, that would be even better if you can generate
> the local rows of the matrix in each processor. If not, communicating
> the matrix row from the 'master' to the 'slaves' could be a real
> bootleneck (large data to compute at the master while slaves waiting,
> large data to scatter from master to slaves), If you cannot avoid
> dense matrices, then you should try hard to compute the local rows at
> the owning processor.
>
>
>>
>> On Mon, Sep 22, 2008 at 6:51 PM, Lisandro Dalcin <dalcinl at gmail.com> wrote:
>>>
>>> Well, any iterative solver will actually work, but expect a really
>>> poor scalability :-). I believe (never used dense matrices) that you
>>> could use a direct method (PLAPACK?), but again, be prepared for long
>>> running times if your problem is (even moderately) large.
>>>
>>> On Mon, Sep 22, 2008 at 10:35 PM, Yujie <recrusader at gmail.com> wrote:
>>> > To my knowledge, PETsc doesn't provide parallel dense matrix-based
>>> > solvers,
>>> > such as for CG, GMRES and so on. If it is, how to deal with this
>>> > problem?
>>> > Thanks.
>>> >
>>> > Regards,
>>> >
>>> > Yujie
>>> >
>>>
>>>
>>>
>>> --
>>> Lisandro Dalcín
>>> ---------------
>>> Centro Internacional de Métodos Computacionales en Ingeniería (CIMEC)
>>> Instituto de Desarrollo Tecnológico para la Industria Química (INTEC)
>>> Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)
>>> PTLC - Güemes 3450, (3000) Santa Fe, Argentina
>>> Tel/Fax: +54-(0)342-451.1594
>>>
>>
>>
>
>
>
> --
> Lisandro Dalcín
> ---------------
> Centro Internacional de Métodos Computacionales en Ingeniería (CIMEC)
> Instituto de Desarrollo Tecnológico para la Industria Química (INTEC)
> Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)
> PTLC - Güemes 3450, (3000) Santa Fe, Argentina
> Tel/Fax: +54-(0)342-451.1594
>
>



-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which
their experiments lead.
-- Norbert Wiener