The param.ccl File

Users control the operation of thorns via parameters given in a file at runtime. The param.ccl file is used to specify the parameters used to control an individual thorn, and to specify the values these parameters are allowed to take. When the code is run, it reads a parameter file and sets the parameters if they fall within the allowed values. If a parameter is not assigned in a parameter file, it is given its default value.

There are three access levels available for parameters:

Global

These parameters are seen by all thorns.

Restricted

These parameters may be used by other implementations if they so desire.

Private

These are only seen by this thorn.

A parameter specification consists of:

• The parameter type (each may have an optional CCTK_ in front)

  REAL

  INT

  KEYWORD

  A distinct string with only a few known allowed values.

  STRING

  An arbitrary string, which must conform to a given regular expression.

  BOOLEAN

  A boolean type which can take values 1, t, true, yes or 00, f, false, no.

• The parameter name

• An optional size (in square brackets)-if this is present, the parameter is a ``parameter array'', i.e. it will actually be an array of parameters, each of which has the same properties, but a different value. Such arrays appear as normal arrays in C or Fortran, 0-based in C, and 1-based in Fortran. In the parameter file the value of each element is specified with square brackets and is 0-based. The size must be an integer.

• A description of the parameter

• An allowed value block-this consists of a brace-delimited block of lines^part71describing the allowed values of the parameter. Each range may have a description associated with it by placing a :: on the line, and putting the description afterwards.

• The default value-this must be one of the allowed values.

For the numeric types INT and REAL, a range consists of a string of the form lower-bound:upper-bound:step, where a missing number or an asterisk `*' denotes anything (i.e. infinite bounds or an infinitesimal step).

For example,

REAL Coeff "Important coefficient"
{
0:3.14 :: "Range has to be from zero to Pi, default is zero"
} 0.0

#No need to define a range for BOOLEAN
BOOLEAN nice "Nice weather?"
{
}"yes"

# A example for a set of keywords and its default (which has to be
# defined in the body)
KEYWORD confused "Are we getting confused?"
{
  "yes"    :: "absolutely positively"
  "perhaps" :: "we are not sure"
  "never"   :: "never"
} "never"

REAL Length[2] "Length in each direction"
{
0:* :: "Range has to be from zero to infinity, default is one"
} 1.0

defines a REAL parameter, a BOOLEAN parameter, a KEYWORD, and an array of REAL parameters.

By default, all parameters are private; to change this, an access specification of the form global: or restricted: (or private: to change it back) may be placed on a line by itself. This changes the access level for any parameter defined in the file from that point on.

To access restricted parameters from another implementation, a line containing shares: <name> declares that all parameters mentioned in the file, from now until the next access specification, originate in implementation <name>. (Note that only one implementation can be specified on each shares: line.) Each of these parameters must be qualified by the initial token USES or EXTENDS, where

USES

indicates that the parameters range remains unchanged.

EXTENDS

indicates that the parameters range is going to be extended.

In contrast to parameter declarations in other access blocks, the default value must be omitted--it is impossible to set the default value of any parameter not originating in this thorn. For example, the following block adds possible values to the keyword initial_data originally defined in the implementation einstein, and uses the REAL parameter speed.

shares:einstein

EXTENDS KEYWORD initial_data
{
  "bl_bh"         :: "Brill Lindquist black holes"
  "misner_bh"     :: "Misner black holes"
  "schwarzschild" :: "One Schwarzschild black hole"
}

USES CCTK_REAL speed

Note that you must compile at least one thorn which implements einstein.