[Trilinos-Users] [EXTERNAL] Re: Xpetra wrappers around existing Tpetra objects

[Andrey Prokopenko]

Hi Martin,

If "MueLu as a solver' you mean a standalone solver, then you just need 
to add the following lines to what Jonathan wrote:

Tpetra::MultiVector<> rhs, initial_guess;
int max_its = 40;

M->IsPreconditioner(false);
M->Iterate(rhs, initial_guess, max_its);

-Andrey

On 06/03/2016 10:43 AM, Martin Vymazal wrote:
> Hello Jonathan,
>
>  thank you very much, this helps. I think that's all I need, but I was 
> wondering about one more thing - is there a similarly easy way to use 
> MueLu as a solver?
>
> Best regards,
>
>  Martin
>
>
> On 2016-06-03 17:28, Jonathan Hu wrote:
>> Hi Martin,
>>
>>     Yes, there are easier ways to use MueLu with an existing
>> Tpetra::CrsMatrix.  You do not need to convert to Xpetra. Something
>> like this will work in your case:
>>
>> Teuchos::RCP<Tpetra::CrsMatrix<> > A;
>> ParameterList paramList;
>> //set the MueLu options
>> Teuchos::RCP<MueLu::TpetraOperator> M =
>> MueLu::CreateTpetraPreconditioner(A, paramList);
>>
>> M is a Tpetra::Operator and can be used directly with Belos.
>>
>> This is described in more detail in the user's guide
>> (muelu/doc/UsersGuide/mueluguide.pdf) on page 22.  Thank you for the
>> feedback on the documentation ... I'll see if we can make the
>> migration path clearer for first-time users.
>>
>> Regards,
>> Jonathan
>>
>> Martin Vymazal wrote on 06/03/2016 08:10 AM:
>>> Hello,
>>>
>>>  I have an RCP pointer to Tpetra::CrsMatrix called A and I would 
>>> like to pass this to MueLu Hierarchy object. It seems that the only 
>>> option is to wrap A, the right-hand side vector and the vector of 
>>> unknows in Xpetra RCP pointers. The following compiles (I found a 
>>> similar code in the MueLU tutorial):
>>>
>>>   Teuchos::RCP<Xpetra::CrsMatrix<>> exA = Teuchos::rcp(new 
>>> Xpetra::TpetraCrsMatrix<>(A));
>>>   Teuchos::RCP<Xpetra::CrsMatrixWrap<>> exAWrap = Teuchos::rcp(new 
>>> Xpetra::CrsMatrixWrap<>(exA));
>>>   RCP<Xpetra::Matrix<>> xpetra_A = 
>>> Teuchos::rcp_dynamic_cast<Xpetra::Matrix<>>(exAWrap);
>>>
>>>   MueLu::Hierarchy<Scalar, LocalOrdinal, GlobalOrdinal> H(xpetra_A);
>>>   H.SetDefaultVerbLevel(MueLu::Medium);
>>>
>>> Could you please confirm that the first line only creates a shallow 
>>> copy of A? Is there any easier/more correct/more elegant way of 
>>> constructing xpetra_A? I'm also stuck at this point, because now I 
>>> need Xpetra-style pointers to the map that was used to construct 
>>> (Tpetra) A in order to construct Xpetra-style right-hand side 
>>> multivector (or pointer to it). How do I get Xpetra vectors from 
>>> Tpetra vectors, given the fact that the map of A is a Tpetra map?
>>>
>>> Thank you for your help.
>>>
>>>  Martin
>>>
>>> P. S. MueLu looks interesting, but the documentation (especially the 
>>> Xpetra part) could be a bit more extensive ... It looks like there's 
>>> a lot of attention paid to users who migrate from Epetra to Tpetra, 
>>> but what about those, who already have codebase which is exclusively 
>>> Tpetra-based? Are they supposed to move everything to Xpetra in 
>>> order to be able to use MueLu?
>>> _______________________________________________
>>> Trilinos-Users mailing list
>>> Trilinos-Users at trilinos.org
>>> https://trilinos.org/mailman/listinfo/trilinos-users
>>>
>>
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