[Trilinos-Users] [EXTERNAL] Re: AMG Preconditioner Neumann Laplacian 32 vs 64 bit issue

[Martin Stoll]

Dear Ray,

thanks for the comments.

Yes, the Neumann Laplacian is indeed singular. In fact, from within dealII
I simply use the ML AMG preconditioner as a black box as there are only a
few parameters I can play with. In my case usually, type of smoother,
smoother steps and number of cycles. So I am not really aware what is
happening within ML and I go with all the default settings. I am sorry for
being so ignorant but I never had any problems. Only when I moved my code
to a different machine running 64 bits I was having problems. Again, same
version of dealII and trilinos on my mac runs smoothly.

I will look into changing some options from within deal.II to try a
different solver for the coarse grid and hope for the best.

Thanks again for the comments.

Best,
Martin

2011/12/1 Tuminaro, Raymond S <rstumin at sandia.gov>

>  So, I'm guessing that the Neumann Laplacian is singular.  Are you using
> a direct solve on the coarsest grid? Depending on how things are handled
> here ... you might get different results. You might try switching to an
> iterative method on the coarsest level and see what happens.
>
> -Ray
>
>  ------------------------------
> *From:* trilinos-users-bounces at software.sandia.gov [
> trilinos-users-bounces at software.sandia.gov] on behalf of Martin Stoll [
> martin.stoll80 at gmail.com]
> *Sent:* Thursday, December 01, 2011 4:29 AM
> *To:* Alberto F. Martín-Huertas
> *Cc:* trilinos-users at software.sandia.gov
> *Subject:* [EXTERNAL] Re: [Trilinos-Users] AMG Preconditioner Neumann
> Laplacian 32 vs 64 bit issue
>
>  Hi Alberto,
> thanks for your comment.
>
> I just tried the Dirichlet Laplacian on  the velocity space, the Neumann
> Laplacian was on the pressure space, and that worked fine.
>
> As I said on my laptop and the 32 bit desktop everything work but when I
> switch to the 64 bit machine the outcome is quite different. Our software
> engineer also tried different versions of trilinos (currently 10.4.2, which
> is recommended by the deal.II developers). My Desktop uses trilinos 9.03
> and my laptop 10.4.2 and they both work fine.
>
> Any help is greatly appreciated.
>
> Best,
> Martin
>
> 2011/12/1 Alberto F. Martín-Huertas <amartin at cimne.upc.edu>
>
>>  Hi Martin,
>>
>>  did you observe the same behaviour with a
>>  Dirichlet Laplacian ?
>>
>>  Best regards,
>>  Alberto.
>>
>>  On Thu, 1 Dec 2011 12:52:08 +0100, Martin Stoll wrote:
>> > Hi all,
>> >
>> > I am using deal.II and from there call the ML AMG preconditioner. I
>> > am using it to approximate a Neumann Laplacian, which works like a
>> > charm on
>> > my 32 bit desktop Ubuntu machine and also on my Mac Book Pro running
>> > Snow Leopard. Now copying this to a linux 64 bit machine I get weird
>> > results meaning
>> >  that applying the preconditioner results
>> > 32 bit
>> > norm(vin)=0.01
>> > APPLY AMG
>> > norm(vout)=0.15
>> >
>> > 64 bit
>> > norm(vin)=0.01
>> >  APPLY AMG
>> >  norm(vout)=1e+11
>> >
>> > When instead of the Neumann Laplacian I put a mass matrix into the
>> > AMG routine the blow does not happen.
>> >
>> > I am not sure where to go from here so I hope I could get some help
>> > here.
>> >
>> > Best,
>> >  Martin
>> >
>> > --
>> > Martin Stoll
>> > Postdoctoral Research Fellow
>> >
>> > Computational Methods in Systems and Control Theory
>> >
>> > Max Planck Institute for Dynamics of Complex Technical Systems
>> > Sandtorstr. 1, D-39106 Magdeburg,Germany
>>  > Email: martin.stoll80 at gmail.com [1]
>> > URL: http://www.mpi-magdeburg.mpg.de/mpcsc/stollm/ [2]
>> >
>> > Tel :+49 391 6110 384
>> >
>> >
>> >
>>  > Links:
>> > ------
>> > [1] mailto:stollm at mpi-magdeburg.mpg.de
>> > [2] http://www.mpi-magdeburg.mpg.de/mpcsc/stollm/
>>
>> --
>>  Alberto F. Martín-Huertas
>>  Centre Internacional de Mètodes Numèrics a l'Enginyeria (CIMNE)
>>  Parc Mediterrani de la Tecnologia, UPC
>>  Esteve Terrades 5, Building C3, Office 210,
>>  08860 Castelldefels (Barcelona, Spain)
>>  Tel.: (+34) 9341 34223
>>  e-mail: amartin at cimne.upc.edu
>>
>>  ________________
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>>
>>
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>
>
>
> --
> Martin Stoll
> Postdoctoral Research Fellow
>
> Computational Methods in Systems and Control Theory
> Max Planck Institute for Dynamics of Complex Technical Systems
> Sandtorstr. 1, D-39106 Magdeburg,Germany
> Email: martin.stoll80 at gmail.com <stollm at mpi-magdeburg.mpg.de>
>
> URL: http://www.mpi-magdeburg.mpg.de/mpcsc/stollm/
>
> Tel :+49 391 6110 384
>
>


-- 
Martin Stoll
Postdoctoral Research Fellow

Computational Methods in Systems and Control Theory
Max Planck Institute for Dynamics of Complex Technical Systems
Sandtorstr. 1, D-39106 Magdeburg,Germany
Email: martin.stoll80 at gmail.com <stollm at mpi-magdeburg.mpg.de>
URL: http://www.mpi-magdeburg.mpg.de/mpcsc/stollm/

Tel :+49 391 6110 384
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