[Users] Phone Call Mon, Nov 8th

[Peter Diener]

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