[Users] Phone Call Mon, Nov 8th

[Erik Schnetter]

I tested further, using Carpet instead of PUGH. I believe that the problem
is in the single processor case of PUGHInterp, i.e. that the 2 process
results are actually correct. Carpet gives identical answers for 1 and 2
processes.

-erik

On Mon, Nov 8, 2010 at 8:03 AM, Peter Diener <diener at cct.lsu.edu> wrote:

> Hi,
>
> > 1) Testsuites
> > A lot has been done over the course of last week, and I would like to
> > thank all involved people. A few issues remain however:
> >  1a) Most AHFinderDirect testsuites fail on 2 processes. This is not
> >      new. This has been the same for last release. However, in contrast
> >      to some other thorns, AHFinderDirect is used by almost every
> >      group, in production simulations. We should really figure out what
> >      goes wrong here. Even more severe: preliminary tests suggest that
> >      this could be connected to the interpolator, which would make
> >      matters only worse if it turns out to be true.
>
> I took a bit closer look at this trying to figure out if the problem is
> with the interpolator or not. Defining in gr/expansion.cc:
>
> #define GEOMETRY_INTERP_DEBUG2
>
> and changing the output formatting from using %g to %15.11g to get more
> digits in the debug output it was clear that there was differences in the
> interpolation results (of the order 1e-5) when running the test parameter
> file Kerr-definition-expansion.par on 1 or 2 processors, even though the
> interpolation points were identical.
>
> That parameter file uses the interpolation parameters:
>
> AHFinderDirect::geometry_interpolator_name = "Lagrange polynomial
> interpolation"
> AHFinderDirect::geometry_interpolator_pars = "order=4"
>
> I see the same when using:
>
> AHFinderDirect::geometry_interpolator_name = "Lagrange polynomial
> interpolation"
> AHFinderDirect::geometry_interpolator_pars = "order=2"
>
> while the following combinations all give identical bh masses on 1 or 2
> processors:
>
> AHFinderDirect::geometry_interpolator_name = "Lagrange polynomial
> interpolation"
> AHFinderDirect::geometry_interpolator_pars = "order=3"
>
> AHFinderDirect::geometry_interpolator_name = "Hermite polynomial
> interpolation"
> AHFinderDirect::geometry_interpolator_pars = "order=2"
>
> AHFinderDirect::geometry_interpolator_name = "Hermite polynomial
> interpolation"
> AHFinderDirect::geometry_interpolator_pars = "order=3"
>
> In those cases the largest differences between 1 and 2 processor runs seem
> to be of order 1e-13.
>
> So it seems there is a bug in AEILocalInterp in the 4th and 2nd order
> Lagrange interpolation schemes, while the 3rd order Lagrange interpolation
> and 2nd and 3rd order Hermite interpolation schemes are okay.
>
> Does anybody feel up to looking into this?
>
> Cheers,
>
>   Peter
>
>
>
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-- 
Erik Schnetter <schnetter at cct.lsu.edu>   http://www.cct.lsu.edu/~eschnett/
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