[petsc-users] "Must select a target sorting criterion if using shift-and-invert"

[Matthew Knepley]

On Mon, Oct 23, 2017 at 11:18 AM, Jose E. Roman <jroman at dsic.upv.es> wrote:

> Changed. Hope it is clear now.
> https://bitbucket.org/slepc/slepc/commits/511900656a27a161c1df6fe2e42fd8
> d66d071800


Great, that is much clearer.

  Thanks,

     Matt


>
> Jose
>
> > El 21 oct 2017, a las 14:27, Matthew Knepley <knepley at gmail.com>
> escribió:
> >
> > On Sat, Oct 21, 2017 at 2:20 AM, Jose E. Roman <jroman at dsic.upv.es>
> wrote:
> > This was added in 3.8 to check the common case when people incorrectly
> sets shift-and-invert with EPS_SMALLEST_MAGNITUDE. To compute smallest
> eigenvalues with shift-and-invert the correct way is to set target=0 and
> which=EPS_TARGET_MAGNITUDE. See for instance
> > http://slepc.upv.es/documentation/current/src/eps/
> examples/tutorials/ex13.c.html
> >
> > Jose, one thing we are trying to do in PETSc now is to give the options
> to fix a problem (or at least representative options)
> > directly in the error message. Or maybe a pointer to the relevant manual
> or tutorial section. This gives users a hand up.
> >
> >   Thanks,
> >
> >      Matt
> >
> >
> > Jose
> >
> >
> > > El 21 oct 2017, a las 1:51, Matthew Knepley <knepley at gmail.com>
> escribió:
> > >
> > > On Fri, Oct 20, 2017 at 7:43 PM, Kong, Fande <fande.kong at inl.gov>
> wrote:
> > > Hi All,
> > >
> > > I am trying to solve a generalized eigenvalue problem (using SLEPc)
> with "-eps_type krylovschur -st_type sinvert". I got an error message:
> "Must select a target sorting criterion if using shift-and-invert".
> > >
> > > Not sure how to proceed.  I do not quite understand this sentence.
> > >
> > > You need to know how to choose the shift. So for instance you want the
> smallest eigenvalues, or the closest to zero, etc.
> > > I don't know the options, but they are in the manual.
> > >
> > >    Matt
> > >
> > >
> > > Fande,
> > >
> > >
> > >
> > > --
> > > 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/
> >
> >
> >
> >
> > --
> > 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/
>
>


-- 
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.caam.rice.edu/~mk51/>
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