Cactus Parameters

Parameters are the means by which the user specifies the runtime behaviour of the code. Each parameter has a data type and a name, as well as a range of allowed values and a default value. These are declared in the thorn's param.ccl file.

The thorn determines which parameters can be used in other thorns by specifying a scope for the thorn, as explained in Section B5.2.

The user may specify initial values for parameters in the parameter file (see Section A3.2); the flesh validates these values against the parameters' allowed ranges. Otherwise, the initial value of the parameter is taken to be its default. Once validated, parameter values are fixed, and cannot be changed, unless the parameter is specified to be steerable (see B5.3). For a detailed discussion of the param.ccl syntax, see Appendix E2.3.

The full specification for a parameter declaration is

[EXTENDS|USES] <parameter_type>[[<size>]] <parameter name> "<parameter description>"
{
  <PARAMETER_RANGES>
} <default value>

You can obtain lists of the parameters associated with each thorn using the Cactus command line options -o and -O (Section A3.1).