[petsc-users] STFILTER in slepc

[Matthew Knepley]

On Wed, Oct 10, 2018 at 8:41 PM Moritz Cygorek <mcygorek at uottawa.ca> wrote:

> Thank you very much. Apparently, I've misunderstood what the filter
> actually does. I thought about the much simpler process, where you
> diagonalize
>
>
> -(A- tau*I)^2 +offset*I
>
>
> where tau is my target an offset is large enough so that the global
> maximum is reached for eigenvalues around tau.
>

Is this different from -eps_target_magnitude?

  Thanks,

    Matt


> Then you look for the largest eigenvalue of the modified problem and
> either calculate the Ritz value of the original matrix or calculate back
> from the eigenvalues of the modified problem.
>
>
> Now, it looks to me like -st_type filter activates something like the
> package FILTLAN.
>
>
> I guess I can define a MatShell to do the thing I intended in the first
> place.
>
> But, I guess, this is a common thing, so I am wondering whether it is
> already implemented somewhere and I just didn't find it in the
> documentation.  Can you say something about this?
>
>
> Regards,
>
> Moritz
>
>
>
>
> ------------------------------
> *From:* Jose E. Roman <jroman at dsic.upv.es>
> *Sent:* Wednesday, October 10, 2018 3:48 PM
> *To:* Moritz Cygorek
> *Cc:* petsc-users at mcs.anl.gov
> *Subject:* Re: [petsc-users] STFILTER in slepc
>
> This type of method requires a very high degree polynomial; suggest using
> degree=100 at least (this is the default value), but larger values may be
> necessary. Also, for this particular filter the "range" must be
> approximately equal to the numerical range; if you have no clue where your
> first and last eigenvalues are, you may use EPSSolve() calls with
> EPS_LARGEST_REAL and EPS_SMALLEST_REAL.
>
> Jose
>
> > El 10 oct 2018, a las 21:10, Moritz Cygorek <mcygorek at uottawa.ca>
> escribió:
> >
> > Thank you for the fast reply.
> >
> > I've tried running my program (using the defaul Krylov-Schur method for
> sparse MPI matrices) with the additional options:
> >
> > -st_type filter -st_filter_degree 2 -st_filter_interval 2.,2.7
> -st_filter_range -2000,2000
> >
> > and I get the following error message:
> >
> > [0]PETSC ERROR: STFILTER cannot get the filter specified; please adjust
> your filter parameters (e.g. increasing the polynomial degree)
> > ....
> > [0]PETSC ERROR: #1 FILTLAN_GetIntervals() line 451 in
> /home/applications/sources/libraries/slepc-3.9.2/src/sys/classes/st/impls/filter/filtlan.c
> > [0]PETSC ERROR: #2 STFilter_FILTLAN_setFilter() line 1016 in
> /home/applications/sources/libraries/slepc-3.9.2/src/sys/classes/st/impls/filter/filtlan.c
> > [0]PETSC ERROR: #3 STSetUp_Filter() line 42 in
> /home/applications/sources/libraries/slepc-3.9.2/src/sys/classes/st/impls/filter/filter.c
> > [0]PETSC ERROR: #4 STSetUp() line 271 in
> /home/applications/sources/libraries/slepc-3.9.2/src/sys/classes/st/interface/stsolve.c
> > [0]PETSC ERROR: #5 EPSSetUp() line 263 in
> /home/applications/sources/libraries/slepc-3.9.2/src/eps/interface/epssetup.c
> > [0]PETSC ERROR: #6 EPSSolve() line 135 in
> /home/applications/sources/libraries/slepc-3.9.2/src/eps/interface/epssolve.c
> >
> >
> >
> > Do you have a clue what I've missed?
> >
> >
> > Moritz
> >
> >
> > From: Jose E. Roman <jroman at dsic.upv.es>
> > Sent: Wednesday, October 10, 2018 2:30 PM
> > To: Moritz Cygorek
> > Cc: petsc-users at mcs.anl.gov
> > Subject: Re: [petsc-users] STFILTER in slepc
> >
> >
> > > El 10 oct 2018, a las 19:54, Moritz Cygorek <mcygorek at uottawa.ca>
> escribió:
> > >
> > > Hi,
> > >
> > > in the list of changes to SLEPc version 3.8, it is stated that there
> is a preliminary implementation of polynomial filtering using STFILTER.
> > >
> > > Because I am struggling to obtain interior eigenvalues and harmonic
> extraction seems not to be stable enough in my case, I wanted to give it a
> try, but I could not find any documentation yet.
> > >
> > > Does anybody have an example of how to use STFILTER or any
> documentation about it?
> > >
> > > Thanks in advance,
> > > Moritz
> >
> > There are no examples. You just set the type to STFILTER and set some
> parameters such as the interval of interest or the polynomial degree. See
> functions starting with STFilter here:
> http://slepc.upv.es/documentation/current/docs/manualpages/ST/index.html
> >
> > In some problems it works well, but don't expect too much. It is still
> in our to-do list to make it more usable. It will be good to have your
> feedback. If you want, send results to slepc-maint, maybe we can help
> tuning the parameters.
> >
> > Jose
>
>

-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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