[Trilinos-Users] ansazi question

[Alicia Klinvex]

Sorry, I've been traveling.  I have an example file of how to do this; I'll
comment it and send it to you after I get back.

- Alicia

On Fri, Feb 13, 2015 at 8:03 PM, Hysom, David A. <hysom1 at llnl.gov> wrote:

>  Alicia,
>
>  I polled my collegues, some whom are are computer scientists, others are
> more
> math inclined, and was rather surprised at their quick replies:
>
>  Andy Yoo: "I would say definitely yes too."
>
>  Geoff Sanders: "Yeah, I think we need it.    Dynamic graphs it would be
> useful for, too ... It's extremely useful to a numerical analyst that seeks
> to understand what error modes an algorithm is struggling with."
>
>  Lance Ward: "I would vote yes since it is very hard to know in advance
> what the smallest tolerance you'll be able to obtain is and on the
> assumption it is better to give the customer some results which may be less
> than ideal and a warning about it vs giving them nothing like we currently
> do if it fails?"
>
>  regards, David
>  ------------------------------
> *From:* trilinos-users-bounces at software.sandia.gov [
> trilinos-users-bounces at software.sandia.gov] on behalf of Hysom, David A. [
> hysom1 at llnl.gov]
> *Sent:* Friday, February 13, 2015 3:44 PM
> *To:* Alicia Klinvex
>
> *Cc:* trilinos-users at software.sandia.gov
> *Subject:* Re: [Trilinos-Users] ansazi question
>
>   Alicia,
>
>  Thanks for your quick response. Yes, we'd really like to do this.
>
>  FYI, we're performing iterative spectral clustering:
>   - compute the 2nd smallest eigenvector
>   - use it to determine how to split the graph (of the matrix) into two
> sub-graphs
>   - recurse for each subgraph, until some stopping criteria is met
>
>  A question is: what is the "best" thing to do if we get convergence
> failure
> at some point, on one of the sub-graphs? In the past, we've thrown an
> exception.
> Currently, we print out an error message and continue processing whatever
> sub-graphs are still to be split (and don't attempt to split the
> sub-graph for which
> convergence was not achieved). What we'd like to experiment with:
> retrieve the eigenvectors, even if not converged, and run some
> statistical tests
> to determine if they're "good enough" to provide a reasonable splitting.
>
>  - David
>
>  ------------------------------
> *From:* Alicia Klinvex [aklinvex at purdue.edu]
> *Sent:* Friday, February 13, 2015 3:29 PM
> *To:* Hysom, David A.
> *Cc:* trilinos-users at software.sandia.gov
> *Subject:* Re: [Trilinos-Users] ansazi question
>
>   Hello David,
>
>  There is a way to retrieve the eigenpairs if convergence fails, but it's
> not easy.  The issue is that you use the LOBPCGSolMgr, I assume, which does
> not give you access to the solver.  The solver has a function to return the
> Ritz values and vectors; the solver manager does not.  You would need to
> create a custom debug status test (which allows you to grab the solver) and
> provide it to the solver manager.  This is not something that we generally
> recommend doing, but if you desperately want to do so, I can give you more
> information about how to do this.
>
>  Best wishes,
> Alicia
>
> On Fri, Feb 13, 2015 at 6:14 PM, Hysom, David A. <hysom1 at llnl.gov> wrote:
>
>>  Hi,
>>
>>  We're using anasazi's LOBPCG, and have cases where convergence
>> fails, but we'd still like to retrieve the 2nd smallest eigenvector (we're
>> computing the smallesBasicEigenproblemt two). When we call:
>>
>>  Anasazi::Eigensolution<scalar_t, mvec_t> sol = problem->getSolution();
>> Teuchos::RCP<mvec_t> evecs = sol.Evecs;
>> cout << "evecs.size: " << evecs->getNumVectors() << endl;
>>
>>  we get a single vector. However, since anasazi can print out the
>> eigenvalues and residuals after every iteration, I'm guessing there
>> should be a way to retrieve the eigenpairs if convergence fails.
>>
>>  So, is there? If not, how easy would it be to modify the code to
>> do so, and where should I start?
>>
>>  thanks, David
>>
>> _______________________________________________
>> Trilinos-Users mailing list
>> Trilinos-Users at software.sandia.gov
>> https://software.sandia.gov/mailman/listinfo/trilinos-users
>>
>>
>
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