[Trilinos-Users] Sparse matrix and Anasazi Solvers,

[Mike Atambo]

Alicia,
Im still trying to figure  out what exactly im facing. Maybe what you
described be the issue, but  at this
point i would prefer to try out what you have suggested, if it works, then
it would be certain thats what im facing,
if not, then i can rule that out.
Please let me know how to  set the krylov-shur  solver   as you suggested,
here are the parameters i pass to  the anasaziPL   for Krylov-Shur at the
moment:

  const double tol = 1.0e-8;
  const int maxIters = 500;
  anasaziPL.set ("Which", "SR");
  anasaziPL.set ("Block Size",1 );
  //anasaziPL.set ("Maximum Iterations", maxIters);
  anasaziPL.set ("Convergence Tolerance", tol);
  anasaziPL.set ("Full Ortho", true);
  anasaziPL.set ("Use Locking", true);

Mike.


On Thu, Feb 5, 2015 at 5:47 PM, Alicia Klinvex <aklinvex at purdue.edu> wrote:

> Hi Mike,
>
> If ARPACK is working for you and block Krylov-Schur is not, I suspect that
> one is using a spectral transformation and the other is not.
>
> I don't know much about scipy's eigs, but I assume it is similar to
> Matlab's eigs (which also uses ARPACK).  When you ask Matlab's eigs to find
> the smallest eigenvalues of a matrix, it will automatically transform the
> problem of finding the smallest eigenpairs of A x = \lambda x into the
> equivalent problem of finding the largest eigenpairs of A^{-1} x =
> \lambda^{-1}x.  Anasazi's Krylov Schur does not do that unless you
> explicitly tell it to.  Could that be the problem you're having?  If so, we
> can discuss how to tell Krylov-Schur that's what you want to do.
>
> Best wishes,
> Alicia Klinvex
>
> On Thu, Feb 5, 2015 at 11:21 AM, Mike Atambo <mikeat4999 at gmail.com> wrote:
>
>> Hi,
>> Im unable to get matrices,  ( say a sparse matrix with
>> 885500 non zeros  out of  about  2822796900 )   to converge
>> with the block davison or the krylov solver,
>>
>> I had a look at the condition number reported by the 'ILUT'
>> preconditioner and it seems to grow rather quickly for my  problems,  ( 9x9
>>  with 39 non zeros has  condition number= 10,   and at    25*25 and 100 non
>> zeros the condition number is at 250).
>>
>> Im able to solve all these examples here using scipy.sparse.eigs  (it
>> uses ARPACK),  so there is probably something that im not doing right.
>>
>> The block-davidson solver with 'ILUT' pre-conditioner   work for the
>> small systems above,   but  beyond  300*300 matrix size,  this is not
>> longer true.
>>
>> At the moment im  following these steps.
>>
>> 1.  Create and initialize a matrix,
>> 2.  Create an anasazi basic eigenproblem,
>> 3.  Create a  solver (either block davidson or krylov-shur)
>> 4.   Get solution,
>>
>> Id like to find out whether there is a way to tell why the system  im
>> working on seems
>> to be  unable to converge.  Any help would be appreciated.
>>
>> Mike
>>
>>
>> --
>> M. O. Atambo
>> mikeat4999 at gmail.com
>> matambo at ictp.it
>> Ext .139
>>
>>
>>
>> _______________________________________________
>> Trilinos-Users mailing list
>> Trilinos-Users at software.sandia.gov
>> https://software.sandia.gov/mailman/listinfo/trilinos-users
>>
>>
>


-- 
M. O. Atambo
mikeat4999 at gmail.com
matambo at ictp.it
Ext .139
Room 209.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://software.sandia.gov/pipermail/trilinos-users/attachments/20150205/2be2c4ec/attachment.html>