[Trilinos-Users] Sparse matrix and Anasazi Solvers,

[Mike Atambo]

On Thu, Feb 5, 2015 at 8:27 PM, Mike Atambo <mikeat4999 at gmail.com> wrote:

> Alicia,
> I will take a look at that  try it on my problem
> thanks,
> Mike
>
> On Thu, Feb 5, 2015 at 8:22 PM, Alicia Klinvex <aklinvex at purdue.edu>
> wrote:
>
>> Hello Mike,
>>
>> I'm pretty sure your Trilinos code is NOT using shift-and-invert with
>> BKS.  (Shift-and-invert is the spectral transformation I described before.)
>>  If you want to use shift-and-invert, you must construct the linear solver
>> yourself and give it to the BKS solver manager.  Some examples of that can
>> be found on this page:
>> http://trilinos.org/docs/r11.12/packages/anasazi/doc/html/examples.html
>>
>> If you want to use a sparse factorization, then the Amesos example should
>> be of interest to you.  If you want to use a preconditioned Krylov method
>> to solve the linear systems that arise at each iteration of BKS, then look
>> at the Belos example.  Let me know if those examples don't make sense to
>> you.
>>
>> Best wishes,
>> Alicia
>>
>> Disclaimer: I am an external collaborator at Sandia, and I did not write
>> the BKS code.  I can help you with the mechanics of getting things to run,
>> but Heidi Thornquist and Rich Lehoucq (who are also on the user mailing
>> list) would probably know more about how to get good performance out of BKS
>> and block Davidson.
>>
>> On Thu, Feb 5, 2015 at 1:50 PM, Mike Atambo <mikeat4999 at gmail.com> wrote:
>>
>>> 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.
>>>
>>>
>>
>
>
> --
> M. O. Atambo
> mikeat4999 at gmail.com
> matambo at ictp.it
> Ext .139
> Room 209.
>
>


-- 
M. O. Atambo
mikeat4999 at gmail.com
matambo at ictp.it
Ext .139
Room 209.
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