Direct LU solver

[Amit.Itagi at seagate.com]

Thanks for your response. A couple of follow-up questions -

I go over the steps

MatCreate()
MatSetType(MPIAIJ)
MatMPIAIJSetPreallocation()
MatSetType(MATSUPERLU_DIST).

Even though I want to do the direct LU solves repeatedly (with the same
matrix), I don't want the program to do LU factorization repeatedly. I hope
I can get that functionality by using the "SAME_PRECONDITIONER" option
(along with -ksppreonly), while defining the KSP. When the program does the
factorization, does it do it in-place or does it allocate new storage ?
After doing the LU factorization, are the other operations such as
MatMult() preserved ?

Thanks

Rgds,
Amit




                                                                           
             Satish Balay                                                  
             <balay at mcs.anl.go                                             
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             02/29/2008 02:06                                              
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On Fri, 29 Feb 2008, Amit.Itagi at seagate.com wrote:

>
> My woes continue.  Based on the earlier discussions, I implemented the
> matrix as
>
>
//=========================================================================
>
>  //   Option 1
>   ierr=MatCreate(PETSC_COMM_WORLD,&A); CHKERRQ(ierr);
>   ierr=MatSetSizes(A,1,1,2,2); CHKERRQ(ierr);
>
>
>   /*    Option 2
>   PetscInt d_nnz=1, o_nnz=1;
>   ierr=MatCreateMPIAIJ(PETSC_COMM_WORLD,1,1,2,2,0,&d_nnz,0,&o_nnz,&A);
> CHKERRQ(ierr);
>   */
>
>   /*   Option 3
>
>
ierr=MatCreateMPIAIJ(PETSC_COMM_WORLD,1,1,2,2,0,PETSC_NULL,0,PETSC_NULL,&A);

>  CHKERRQ(ierr);
>   */
>
>   ierr=MatSetType(A,MATSUPERLU_DIST); CHKERRQ(ierr);
>   ierr=MatSetFromOptions(A); CHKERRQ(ierr);
>
>   // (After this, I set the values and do the assembly). I then use the
> direct LU solver.
>
>
//============================================================================

>
> Note: I have a simple 2 by 2 matrix (with non-zero values in all 4
places).
> If I use "option 1" (based on Satish's email), the program executes
> successfully. If instead of "option 1", I use "option 2" or "option 3", I
> get a crash.
> If I am not mistaken, options 1 and 3 are the same. Option 2,
additionally,
> does a pre-allocation. Am I correct ?

Nope - Option 3 is same as:

MatCreate()
MatSetType(MPIAIJ)
MatMPIAIJSetPreallocation()
MatSetType(MATSUPERLU_DIST)

[i.e first you are setting type as MPIAIJ, and then changing to
MATSUPERLU_DIST]

What you want is:

MatCreate()
MatSetType(MATSUPERLU_DIST)
MatMPIAIJSetPreallocation()

[Ideally you need MatSuerLU_DistSetPreallocation() - but that would be
same as MatMPIAIJSetPreallocation()]

Satish