GC Tiger Team Meeting: Overview

• Code instabilities
  Both of the main 3D GC codes currently under development exhibit instability at "late times" with Schwarzschild initial data. An apparently similar instability is also seen in the 1d Empire code. The chief immediate goal of this meeting is to (optimistically) "cure" these instabilities or at least (more realistically) to formulate a coherent strategy for treatment of the instabilities. This will involve an in-depth investigation of the nature of the instabilities, information exchange re the details of the finite difference updates, particularly in the near-horizon regime, and extensive discussions concerning the approaches which have been taken so far, and what options remain.
• Coordinate conditions for black hole evolutions
  It is clear that we currently know very little concerning appropriate choices of coordinates for generic black hole evolutions such as the late time dynamics of a binary in-spiral. There are various vague ideas floating around, but the time has come for specific (i.e. mathematical) and complete prescriptions for the lapse and shift for these types of problems. Recognizing that this is a basic problem in relativity, rather than computation, we hope to make maximum use of our "external" participants (Misner, and possibly Eardley) for ideas and insight.
• Potential for merging and/or focusing of currently independent code-development efforts
  This is the most contentious issue, not least since there is currently no general agreement in the Alliance concerning how we should proceed vis a vis 3-d code development for the remainder of the project period.