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

[Matthew Knepley]

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/ <http://www.caam.rice.edu/~mk51/>
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