[petsc-users] Matrix Construction Question

[Adam Byrd]

Changing the matrix types worked. When solving AX=B, X and B have to be
dense and A can be a sparse format? I'd like to avoid storing the identity
as a dense format, if possible. By the way, the man page for MATAIJ says
it's a sparse format
http://www.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-current/docs/manualpages/Mat/MATAIJ.html
.

I must ask, is there somewhere in the documentation I should be looking to
figure these sorts of questions out? I feel like a pest, but I'm not sure
where else to look for answers.


On Thu, Jul 7, 2011 at 12:20 AM, Jed Brown <jedbrown at mcs.anl.gov> wrote:

> On Wed, Jul 6, 2011 at 09:53, Adam Byrd <adam1.byrd at gmail.com> wrote:
>
>> I do not want the transpose, but that is what is coming out as the
>> solution. Both my tests show the correct original matrix, and both yield the
>> transpose of the solution verified against Mathematica and the website from
>> which I pulled the 4x4 matrix in test.cpp. Could it be related to the
>> factoring?
>
>
> The problem is that you are trying to solve with an AIJ matrix instead of a
> DENSE matrix. MatMatSolve() calls MatGetArray(). Since this is serial and
> you preallocated enough for a dense matrix, it goes through with no memory
> errors. The storage format for MATAIJ (that happens to be dense) and
> MATDENSE is transposed, so you see the transpose. If you make the solution
> matrix dense, then it will work correctly.
>
>
> --- a/test.cpp
> +++ b/test.cpp
> @@ -48,7 +48,9 @@ int main(int argc,char **args)
>         ierr = MatAssemblyEnd(identityMat,
> MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
>
>         //Setup inverseMat
> -       ierr = MatDuplicate(testMat, MAT_DO_NOT_COPY_VALUES,
> &inverseMat);CHKERRQ(ierr);
> +       ierr = MatCreate(PETSC_COMM_WORLD, &inverseMat);CHKERRQ(ierr);
> +       ierr = MatSetSizes(inverseMat, PETSC_DECIDE, PETSC_DECIDE, rows,
> columns);CHKERRQ(ierr);
> +       ierr = MatSetType(inverseMat, MATDENSE);CHKERRQ(ierr);
>         ierr = MatAssemblyBegin(inverseMat,
> MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
>         ierr = MatAssemblyEnd(inverseMat,
> MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
>
>
>
> PETSc should be more careful about matching types here.
>
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