[Trilinos-Users] Sparse matrix and Anasazi Solvers,

[Alicia Klinvex]

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
>
>
>
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