Cactus Code Thorn InitBase
Author(s)    : Erik Schnetter
Maintainer(s): Cactus team
Licence      : LGPL
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1. Purpose

Thorn InitBase specifies how initial data are to be set up.  It does
not set up any initial data by itself, nor does it contain any
routines which are to be called.  It is merely a convenient repository
remembering how initial data are to be set up, so that other thorns
can check their actions against this thorn.

There are several possibilities:

1. The initial data thorn sets up data on one time level, while other
   time levels are scratch space.  The time evolution method must
   start up from a single time level.  (This is the default.)

2. The initial data thorn sets up data on exactly one time level, and
   is called once for each active time level.  (This means that the
   initial data thorn can only access the current time level.)

3. The initial data thorn sets up data on exactly two time levels, and
   is called once for each active time level.  (This means that the
   initial data thorn can only access the current and the first past
   time level.)

4. The initial data thorn sets up data on all active time levels.
   (This makes it necessary that the initial data thorn checks the
   number of active time levels.)