The Input File

Before running the code, run time parameters must be set in an Input File.

Usually this file is given the name athinput.problem-name, where problem-name is a string identifier, often the same as the name of the problem-generator, i.e. the function in ./athena/src/prob which is used to initialize the data. For example, the 1D MHD Brio & Wu shocktube test uses the input file athinput.brio-wu. A large number of input files for different tests are provided in ./athena/tst.

Within the input file, parameters are grouped into named blocks, with the name of each block appearing on a single line within angle brackets, for example

<job>
problem_id      = Strat      # problem ID: basename of output filenames
maxout          = 5          # Output blocks number from 1 -> maxout
num_domains     = 1          # number of Domains in Mesh

Block names must always appear in angle brackets on a separate line (blank lines above and below the block names are not required, but can be used for clarity).

Below each block name is a list of parameters, with syntax

parameter-name = value [# comments]

White space after the parameter name, after the `=’, and before the # character is ignored. Everything after (and including) the # character is also ignored. Only one parameter value can appear per line. Comment lines (i.e. a line beginning with #) are allowed for documentation purposes. A maximum number of 256 characters is permitted per line in the input file. Both block names and parameter names are case sensitive.

The input file is read by a very flexible parser written for Athena ./athena/src/par.c. The entire input file is read at the very beginning of the main program, and the parameter names and their values stored in memory. Thereafter, these values can be accessed as necessary by any function at any time during execution. The parser allows the parameter names to appear in any order within a named block, extra (or misspelled) parameter names will be parsed and never used. If a value is requested from the parser but its name does not exist, the parser will print an error message and terminate the program. The parameters may be integers, floating point numbers, or strings, but the input values must be of the right type (for example, strings cannot be used to enter integers). The parser will do automatic type conversion, for example converting floating point numbers to double precision if necessary. Parameter values can also be set at run time through the command line, see Tutorial/Command Line.

Functions defined in par.c to read the input file are described in the section on Problem Generators.