Configuration Files

Cactus Configuration (or CCL) files are the way in which the Cactus Flesh find out information about your thorn. Cactus isn't interested in all the private stuff of your thorn, but it needs to know about things like variables, routines, parameters which will interface with other thorns.

In the Hello World example these files are trivial, since we have no variables, only one routine to schedule, and no parameters (to learn about parameters you could try to add a parameter to this thorn to switch off the output, or to change the number of times the message is printed). The contents of our CCL files are

interface.ccl

implements: helloworld

Each thorn has to give a name to what it does, here we say that we do is called "helloworld". (If you look further into the notion of implementations, you will find that this mechanism allows you to switch between different thorns which provide the same implementation, but for our example this isn't very useful).

param.ccl

There are no parameters in the HelloWorld thorn, so this file is empty.

schedule.ccl

schedule HelloWorld at CCTK_EVOL
{
  LANG: C
} "Print message to screen"

This file instructs Cactus to run the routine called HelloWorld in our thorn during the evolution timebin. Additionally it tells Cactus that the source codee is written in C, and provides a descipion of what the routine does.