[Trilinos-Users] ML: reusing structures

[Eric Marttila]

Nico,
I don't know enough to answer your 2nd and 3rd questions, but regarding your 
first question:  Internally, the MultiLevelPreconditioner class holds a pointer 
to the A matrix.  You are not really passing it 'by value' - it is being 
passed by reference since the MultiLevelPreconditioner constructor is defined 
to take a reference.

Hope this helps.
--Eric

On Thursday, February 09, 2012 06:28:11 am Nico Schlömer wrote:
> Hi,
> 
> I've started to get my hands a little dirty with ML's reusing
> strategies, specifically referring to
> http://trilinos.sandia.gov/packages/docs/dev/packages/ml/doc/html/classML__
> Epetra_1_1MultiLevelPreconditioner.html#a0a5c1d47c6938d2ec1cb9bb710723c1e
> 
> If what I understand from the docs is correct, then
> MultiLevelPreconditioner
> ================= *snip* =================
> // set up matrix A (ptr)
> if ( ML is not build )
> {
>    // set up ML list
>    MlPrec_ = Teuchos::rcp( new ML_Epetra::MultiLevelPreconditioner(
> *A, MLList ) );
> }
> // Solve linear systems with MLPrec, A
> 
> // change values of A, not its pointer
> 
> MlPrec_->ComputePreconditioner();
> // ? MlPrec_->ReComputePreconditioner();
> 
> // Solve more linear systems with MLPrec, A
> ================= *snap* =================
> 
> is what you're supposed to do.
> 
> Three questions about it:
> 
> (a) Out of interest: How is the data of the matrix A handled in ML?
> Are references to it passed around?
>     It seems a bit funny to pass in A by value (*A), but then after
> that the pointer to A can't change.
> (b) There is also ReComputePreconditioner(). What are possible use cases
> for it? (c) ComputePreconditioner runs about twice as long with
> checkFiltering *disabled*. Is this somethings that's supposed to happen?
> 
> Cheers,
> Nico
> 
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-- 
Eric A. Marttila
ThermoAnalytics, Inc.
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