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

Thu Dec 1 09:00:01 MST 2011

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<mailto: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<mailto:martin.stoll80 at gmail.com> [1]
> URL: http://www.mpi-magdeburg.mpg.de/mpcsc/stollm/ [2]
>
> Tel :+49 391 6110 384<tel:%2B49%20391%206110%20384>
>
>
>
> Links:
> ------
> [1] mailto:stollm at mpi-magdeburg.mpg.de<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)
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 Tel.: (+34) 9341 34223<tel:%28%2B34%29%209341%2034223>
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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<mailto:stollm at mpi-magdeburg.mpg.de>

URL: http://www.mpi-magdeburg.mpg.de/mpcsc/stollm/

Tel :+49 391 6110 384

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