LSU, Baton Rouge, Louisiana, April 2004
An Apples with Apples retreat was held at LSU from April 26 to 28, 2004,
in conjunction with a Cactus retreat. We thank all our LSU colleagues,
especially Manuel Tiglio, for their hospitality.
The primary goal of the meeting was to make progress toward writing a report
on the first round of Mexico tests. Similar sessions had previously been held
at AEI among the local participants but in Baton Rouge we benefited from a
wider representation of participating groups. Ian Hawke led a tour of the CVS
output for the first round of Mexico tests. The results were discussed. Then
small work groups were formed which updated the draft paper on the first round
of tests to include analysis, comparisons and conclusions for the robust
stability tests and gauge wave tests. Another work group was formed to clean
up the descriptions of the various BSSN systems, and the large amount of
information on adjusted ADM and BSSN systems. The output of the 'robust' and
'gauge wave' working groups will serve as templates for adding treatments of
the linear wave and Gowdy wave tests to complete the paper. A mailing list
has been created to facilitate the communication about the paper.
Joining the mailing list will be understood as a commitment to
authorship on the Mexico I results paper, and active participating in writing
up the paper. For joining one of the working groups, please send email to the
mex1results mailing list.
Decision on a schedule for completing the paper will be shortly made
after all interested participating groups have been given a final chance
to complete their test data in the CVS.
In the Mexico spirit, there were few formal presentations. The major
topics of discussion outside of the working groups were as follows:
Designing the next round of boundary tests. The working paper on the
next round of boundary tests has been updated in the CVS under
/ApplesWithApples/Papers/Boundaries1. The first round of Mexico tests on
:T3 have been extended to a first round of boundary tests by open one
face of the 3-torus to form a manifold with two T2 boundaries. This isolates
problems due to smooth boundaries by avoiding the sharp edges and
corners posed by cubic boundaries. In the robust stability boundary test
the constraints are not satisfied and all variables requiring boundary data
are given random data. In the linear, gauge and Gowdy wave boundary
tests, the spacetime metric is known so that the correct boundary data
for all variables requiring boundary data can be explicitly prescribed. Thus
these tests can be run independently of a constraint preserving boundary
condition. Addition of a Rindler wedge boundary test is under consideration.
The linear wave test may be dropped if the Stage 1 results show
that nothing essential is learned.
The plan is to carry out preliminary exploration of a number of these
tests to decide whether the suggested parameters and output data are
appropriate. The general agreement is that the tests should be run with
a Runge Kutta update scheme rather than ICN. Examples of boundary
test runs were presented by Bela Szilagyi.
The new organization of the CVS was explained by Sascha Husa.
The redesign of the Apples web page was presented by Maria Babiuc and
future plans were discussed.
Tentative plans for future meetings were made. They include a November
2004 meeting in Potsdam and a Spring 2005 meeting in Cordoba.