[petsc-dev] Two questions about PC Object

[Barry Smith]

On Aug 7, 2011, at 9:17 PM, Gabriele Jost wrote:

> 
> 
> 
> Hello!
> 
> I am working with a user of XSEDE (forerly know as TeraGrid) on converting his code from Scalapack to using PETSc. His physical problem yields matrices which are sparse, but the structure is rather general.
> We have a version going that works very well for one type of problems. I can use MUMPS or SuperLU and I get results which are pretty close to what he gets when using Scalapack. 
> However, I am running into problems with the matrices that correspond to a different problem type. I get results when using MUMPS, but they differ widely from the Scalapack results. With MUMPS I get an error like:
> 
> Error reported by MUMPS in numerical factorization phase: INFO(1)=-1, INFO(2)=359
> 
> I noticed that for the matrix types where I get good results, the nonzeros reported for the PC Object type exactly the number of entries in my input data for the matrix (MPIAIJ format). For the type that does not work, petsc reports more nonzeros than what I enter. The message looks like this:
> 
>   linear system matrix = precond matrix:
>   Matrix Object:
>     type=mpiaij, rows=123120, cols=123120
>     total: nonzeros=59094408, allocated nonzeros=59173613

   What is the number of entries you think you put in? Is it one of the two numbers above? Have you done matrix preallocation?    In the example that works do the two numbers above match, i.e. is the preallocation perfect?

    My first guess is simply that the matrix entries are not going in the correct places? Anyway to test with a very small matrix and -mat_view?


   Barry

> 
> My questions are:
> 
> 1) Does anybody know what the error INFO(1)=-1 means in MUMPS?
> 2) How does PETSc calculate the number of nonzeros for the PC matrix?
> 
> Have banging my head against this problem for a while. Any advice is highly appreciated.
> 
> Many thanks in advance!
> 
> Gabriele Jost
> Texas Advanced Computing Center
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