[Trilinos-Users] [EXTERNAL] Re: direct invertion of a projected matrix (Amesos and Epetra_CrsMatrix?)

[Rajamanickam, Sivasankaran]

Denis,

  As Mike said, the performance may not be what you want. Depending on the problem size, number of MPI ranks and number of factorizations vs number of solvers, you might be better of creating distributed sparse matrix and still use a simple sequential sparse solver (assuming memory is not a bottleneck).  The asymptotic number of operations will come into play very quickly in this case.


-Siva



________________________________
From: Trilinos-Users <trilinos-users-bounces at trilinos.org> on behalf of Heroux, Michael A <maherou at sandia.gov>
Sent: Tuesday, March 21, 2017 6:01 PM
To: Denis Davydov; trilinos-users
Subject: [EXTERNAL] Re: [Trilinos-Users] direct invertion of a projected matrix (Amesos and Epetra_CrsMatrix?)


?*Performance will be quite poor, I think.

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From: Trilinos-Users <trilinos-users-bounces at trilinos.org> on behalf of Heroux, Michael A <maherou at sandia.gov>
Sent: Tuesday, March 21, 2017 6:43 PM
To: Denis Davydov; trilinos-users
Subject: [EXTERNAL] Re: [Trilinos-Users] direct invertion of a projected matrix (Amesos and Epetra_CrsMatrix?)


Denis,


You can store a full matrix as a Epetra_CrsMatrix and use Amesos.  Performance will be quite, I think.?


Can you give more details about the dimensions of the problems?


Also, are you using an optimized BLAS for your LAPACK computations?


Mike


________________________________
From: Trilinos-Users <trilinos-users-bounces at trilinos.org> on behalf of Denis Davydov <davydden at gmail.com>
Sent: Tuesday, March 21, 2017 9:38 AM
To: trilinos-users
Subject: [EXTERNAL] [Trilinos-Users] direct invertion of a projected matrix (Amesos and Epetra_CrsMatrix?)

Dear all,

I would like to have a MPI-parallel inversion of (eventually sparse) matrix of size N being several hundreds.
I put "sparse" in brackets, because for starters i need to consider it full. The matrix represents the
projection of a FE operator on a vector subspace. I guess something similar is probably done in
Anasazi in the context of eigensolvers.

So the main question is if I can use Epetra_CrsMatrix but for now set the sparsity to be full?
If that is possible, i suppose i should be able to use Amesos direct solvers to get LU factorization
of the matrix (say using ScaLAPACK) and then do whatever I want with it.

If there are other classes in Trilinos to do the job better, please let me know.

p.s. currently i do inversion in serial, eventually using Lapack, but this takes too much time.

Sincerely,
Denis.

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