The Outer Boundary Problem
Common Elements to Perturbative and Characteristic Approaches:
+ Construction of the World-tube.
+ Setting Coordinates on the exterior region (Stereo-graphic Coordinates).
+ Supply outer boundary condition to Cauchy evolution.
+ Interpolators to transfer data in and out of the Cauchy domain.
Requirements:
+ 3D Cauchy Codes (ADM & Hyperbolic)
+ 3D Exterior Codes (Characteristic & Perturbative)
+ To handle AMR (Waves cross the matching boundary)
+ General Modules
Tests Performed:
+ Characteristic (3D Flat, 1D GR)
+ Perturbative (2D GR)
+ Common Tests?
+ Most groups use weak-field wave solutions for code testing; these
can be shared for purposes of standardization and avoidance of
duplicated effort.
Accuracy:
+ Quantify the errors from Perturbative approach.
Computational Effort:
+ How expensive is a full 3D Characteristic evolution?
General Conclusions:
+ We should target for a coherent plan.
+ Discuss common tests.
+ The resources spent on the Outer Boundary has been reduced
by the merger of CCM and Wave Extraction areas since because
of the overlap a more coherent effort will be pursued.
+ The boundaries, both inner and outer, are code areas which currently
require the largest concentrated physics and CS effort so it is
reasonable that the alliance should make this a major focus of resources.