[Trilinos-Users] [EXTERNAL] Re: IFPACK preconditioners reordering

[Bradley, Andrew Michael]

Hi Danielle,


Not sure if this is of any use, but aeons ago I wrote some code that reordered the matrix globally before then solving with Aztec using Ifpack. The Isorropia part looks like this:


    Teuchos::ParameterList iso_list;
    // Fill in the list.
    partitioner = Teuchos::rcp(new Isorropia::Epetra::Partitioner(&A->Graph(), iso_list));
    rd = rcp(new Isorropia::Epetra::Redistributor(partitioner));
    A_rd = rd->redistribute(*A.get());
    x_rd = rd->redistribute(x);
    b_rd = rd->redistribute(*b.get());


Then the _rd quantities are used in the subsequent solver/preconditioner setup and solve.

Andrew



________________________________
From: Trilinos-Users <trilinos-users-bounces at trilinos.org> on behalf of Erik Boman <egboman at sandia.gov>
Sent: Thursday, February 18, 2016 1:47 PM
To: dcmaddix at stanford.edu
Cc: trilinos-users at trilinos.org
Subject: [EXTERNAL] Re: [Trilinos-Users] IFPACK preconditioners reordering

Danielle,

In general RCM has been found to be the best ordering for incomplete factorizations, so other orderings may not help you.
Still, to clarify the status in Trilinos:

- Ifpack supports both RCM and Metis (directly without Zoltan, possibly only older versions) so you could try nested dissection easily that way.
- Ifpack ordering only works in parallel as it is embedded within Additive Schwarz (known bug).
- Isorropia can compute orderings using Zoltan but not sure how to pass that to Ifpack. (I have never done it.)
- Going forward, Ifpack2 will use Zoltan2 for reordering and adding more orderings to Zoltan2 is work in progress.

Hope this helps.

Erik

On 02/18/2016 01:08 PM, Heroux, Michael A wrote:
Danielle,

Ifpack supports only Reverse Cuthill-McKee (RCM) and Metis reorderings.

The Isorropia package provides an Epetra interface to Zoltan, and does have orderings based on ParMetis and PT-Scotch, but I don't know of a way to get the orderings to work the Ifpack.  Perhaps one of the Isorropia developers could confirm.

Mike


From: Trilinos-Users <trilinos-users-bounces at trilinos.org<mailto:trilinos-users-bounces at trilinos.org>> on behalf of Danielle Catherine Maddix <dcmaddix at stanford.edu<mailto:dcmaddix at stanford.edu>>
Date: Wednesday, February 17, 2016 at 7:24 PM
To: Trilinos Users <trilinos-users at trilinos.org<mailto:trilinos-users at trilinos.org>>
Subject: [EXTERNAL] [Trilinos-Users] IFPACK preconditioners reordering


Hello,


I was using the IFPACK pre conditioners, with particular interest in IC. I was wondering if there were any built-in Trilinos reordering schemes that could be done for banding on my matrix in the preconditioner calculation.  I know that ILUT and ILUt uses RCM by default. Are there other reordering options, such as nested dissection, which uses Zoltan?


Thank you,

Danielle Maddix



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