[petsc-dev] [petsc-users] Convergence of AMG

[Mark Adams]

On Mon, Oct 29, 2018 at 2:35 PM Smith, Barry F. <bsmith at mcs.anl.gov> wrote:

>
>    Why not just stop it once it is equal to or less than the minimum
> values set by the person.


That is what it does now. It stops when it is below the value given.


> Thus you need not "backtrack" by removing levels but the user still has
> some control over preventing a "tiny" coarse problem. For example in this
> case if the user set a minimum of 1000 it would end up with 642 unknowns on
> the coarse level


Yes, that is what it would do now. I thought you wanted something different.


> which is likely better than 6 or 54.
>



>
>     Barry
>
>
> > On Oct 29, 2018, at 8:27 AM, Mark Adams <mfadams at lbl.gov> wrote:
> >
> >
> >
> > On Sun, Oct 28, 2018 at 4:54 PM Smith, Barry F. <bsmith at mcs.anl.gov>
> wrote:
> >
> >    Moved a question not needed in the public discussions to petsc-dev to
> ask Mark.
> >
> >
> >    Mark,
> >
> >     PCGAMGSetCoarseEqLim - Set maximum number of equations on coarsest
> grid
> >
> >    Is there a way to set the minimum number of equations on the coarse
> grid also? This particular case goes down to 6, 54 and 642 unknowns on the
> coarsest grids when I'm guessing it would be better to stop at 642 unknowns
> for the coarsest level.
> >
> > No, because I don't know how it is going to coarsen I did not want to
> bother with backtracking (I do when there is an error on the coarse grid so
> it would be easy to add this but I don't think it is worth the clutter).
> >
>
>
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