[Trilinos-Users] IFPACK preconditioners reordering

[Erik Boman]

Hi Andrew,

Thanks, that may work but it's not recommended since the Partitioner 
just partitions the matrix into parts and the local ordering within each 
part is not guaranteed. It was meant to redistribute for better load 
balance. There is an Isorropia::Epetra::Orderer class for reordering.

Erik

On 02/18/2016 02:01 PM, Bradley, Andrew Michael wrote:
>
> 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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>

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