[petsc-users] Why use MATMPIBAIJ?

[Matthew Knepley]

On Fri, Jan 22, 2016 at 11:10 AM, Hom Nath Gharti <hng.email at gmail.com>
wrote:

> Thanks Matt.
>
> Attached detailed info on ksp of a much smaller test. This is a
> multiphysics problem.
>

You are using FGMRES/ASM(ILU0). From your description below, this sounds
like
an elliptic system. I would at least try AMG (-pc_type gamg) to see how it
does. Any
other advice would have to be based on seeing the equations.

  Thanks,

    Matt


> Hom Nath
>
> On Fri, Jan 22, 2016 at 12:01 PM, Matthew Knepley <knepley at gmail.com>
> wrote:
> > On Fri, Jan 22, 2016 at 10:52 AM, Hom Nath Gharti <hng.email at gmail.com>
> > wrote:
> >>
> >> Dear all,
> >>
> >> I take this opportunity to ask for your important suggestion.
> >>
> >> I am solving an elastic-acoustic-gravity equation on the planet. I
> >> have displacement vector (ux,uy,uz) in solid region, displacement
> >> potential (\xi) and pressure (p) in fluid region, and gravitational
> >> potential (\phi) in all of space. All these variables are coupled.
> >>
> >> Currently, I am using MATMPIAIJ and form a single global matrix. Does
> >> using a MATMPIBIJ or MATNEST improve the convergence/efficiency in
> >> this case? For your information, total degrees of freedoms are about a
> >> billion.
> >
> >
> > 1) For any solver question, we need to see the output of -ksp_view, and
> we
> > would also like
> >
> >   -ksp_monitor_true_residual -ksp_converged_reason
> >
> > 2) MATNEST does not affect convergence, and MATMPIBAIJ only in the
> blocksize
> > which you
> >     could set without that format
> >
> > 3) However, you might see benefit from using something like PCFIELDSPLIT
> if
> > you have multiphysics here
> >
> >    Matt
> >
> >>
> >> Any suggestion would be greatly appreciated.
> >>
> >> Thanks,
> >> Hom Nath
> >>
> >> On Fri, Jan 22, 2016 at 10:32 AM, Matthew Knepley <knepley at gmail.com>
> >> wrote:
> >> > On Fri, Jan 22, 2016 at 9:27 AM, Mark Adams <mfadams at lbl.gov> wrote:
> >> >>>
> >> >>>
> >> >>>
> >> >>> I said the Hypre setup cost is not scalable,
> >> >>
> >> >>
> >> >> I'd be a little careful here.  Scaling for the matrix triple product
> is
> >> >> hard and hypre does put effort into scaling. I don't have any data
> >> >> however.
> >> >> Do you?
> >> >
> >> >
> >> > I used it for PyLith and saw this. I did not think any AMG had
> scalable
> >> > setup time.
> >> >
> >> >    Matt
> >> >
> >> >>>
> >> >>> but it can be amortized over the iterations. You can quantify this
> >> >>> just by looking at the PCSetUp time as your increase the number of
> >> >>> processes. I don't think they have a good
> >> >>> model for the memory usage, and if they do, I do not know what it
> is.
> >> >>> However, generally Hypre takes more
> >> >>> memory than the agglomeration MG like ML or GAMG.
> >> >>>
> >> >>
> >> >> agglomerations methods tend to have lower "grid complexity", that is
> >> >> smaller coarse grids, than classic AMG like in hypre. THis is more
> of a
> >> >> constant complexity and not a scaling issue though.  You can address
> >> >> this
> >> >> with parameters to some extent. But for elasticity, you want to at
> >> >> least
> >> >> try, if not start with, GAMG or ML.
> >> >>
> >> >>>
> >> >>>   Thanks,
> >> >>>
> >> >>>     Matt
> >> >>>
> >> >>>>
> >> >>>>
> >> >>>> Giang
> >> >>>>
> >> >>>> On Mon, Jan 18, 2016 at 5:25 PM, Jed Brown <jed at jedbrown.org>
> wrote:
> >> >>>>>
> >> >>>>> Hoang Giang Bui <hgbk2008 at gmail.com> writes:
> >> >>>>>
> >> >>>>> > Why P2/P2 is not for co-located discretization?
> >> >>>>>
> >> >>>>> Matt typed "P2/P2" when me meant "P2/P1".
> >> >>>>
> >> >>>>
> >> >>>
> >> >>>
> >> >>>
> >> >>> --
> >> >>> 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
> >> >>
> >> >>
> >> >
> >> >
> >> >
> >> > --
> >> > 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
> >
> >
> >
> >
> > --
> > 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
>



-- 
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
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