Cactus Code Thorn Time
Author(s)    : Gabrielle Allen
Maintainer(s): Cactus team
Licence      : LGPL
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1. Purpose

Thorn Time sets the timestep for the simulation by either

	- setting the timestep directly from a parameter value

	- using a Courant-type condition to set the timestep based
	  on the grid-spacing used.

The Courant condition can be applied either once at the start of the
simulation, or the timestep can be calculated dynamically before each timestep.