[petsc-users] On what condition is useful MPI-based solution?

Takuya Sekikawa sekikawa at msi.co.jp
Wed Jan 13 18:04:50 CST 2010

Dear SLEPc/PETSc team,

On Wed, 13 Jan 2010 09:50:57 +0100
"Jose E. Roman" <jroman at dsic.upv.es> wrote:

> > [Q2]
> > Generally, Is MPI only useful in very large matrix?
> > Now I have to solve eigenvalue problem of 1M x 1M matrix,
> > Should I use MPI-based system?
> For a 1 million matrix I would suggest to run in parallel on an MPI cluster. However, a single computer might be enough if the matrix is very sparse, you need very few eigenvalues, and/or the system has enough memory (but in that case, be prepared for very long response times, depending on how your problem converges).
> Jose

Do you have any example of how many PCs need to solve this level of
problem? and also how many memories do each PC should have?

I would like to know how much resources do I need (PCs, memories)
and how long it takes to solve. (not precisely, rough estimation
is enough)

Problem is 1M x 1M symmetric sparse matrix, and only a few eigenpairs 
(at least 1) I need. so currently I plan to use lanczos or krylov-schur
method, with EPS_NEV=1.

   Takuya Sekikawa
         Mathematical Systems, Inc
                    sekikawa at msi.co.jp

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