Background

So what is this ``CalcTmunu'', anyway? CalcTmunu is a general interface which allows any thorn to `declare' that it contains matter variables, by adding terms to the components of the stress energy tensor. This is done using the Cactus include file mechanism, which allows thorns to contribute code to include files, which can then be included by any thorn which wishes to use them. For CalcTmunu there are two include files^part251, CalcTmunu.inc and CalcTmunu_temps.inc.

In CalcTmunu.inc, one can place code of the form

	Ttt = Ttt + ...
	Ttx = Ttx + ...
	Tty = Tty + ...
	Ttz = Ttz + ...
	Txx = Txx + ...
	Txy = Txy + ...
	Txz = Txz + ...
	Tyy = Tyy + ...
	Tyz = Tyz + ...
	Tzz = Tzz + ...

to add terms to the components $T_{\mu\nu}$. Each of these variables is of type CCTK_REAL. (If you omit the Ttt +, Ttx +, etc. from the right hand sides of these assignment statements then you will be assuming that your thorn is the only one which provides matter degrees of freedom, and excluding contributions from other matter thorns which may be activated.) This code will be executed for each point on the grid, whose indices will be stored in the integers i, j, and k. Currently it must be `fixed form' Fortran code.

CalcTmunu_temps.inc will be included in the variable declaration section for the block of code which contains the

#include "CalcTmunu.inc"

One can put local temporary variable declarations needed for the code above into this file. The Ttt, Ttx, etc. will be declared within a macro from ADMMacros.