The EPOCH input deck

Most of the control of EPOCH is through a text file called input.deck. The input deck file must be in the output directory which is passed to the code at runtime and contains all the basic information which is needed to set up the code, including the size and subdivision of the domain, the boundary conditions, the species of particles to simulate and the output settings for the code. For most users this will be capable of specifying all the initial conditions and output options they need. More complicated initial conditions will be handled in later sections.

The input deck is a structured file which is split into separate blocks, with each block containing several “parameter” = “value” pairs. The pairs can be present in any order, and not all possible pairs must be present in any given input deck. If a required pair is missing the code will exit with an error message. The blocks themselves can also appear in any order. The input deck is case sensitive, so true is always “T”, false is always “F” and the names of the parameters are always lower case. Parameter values are evaluated using a maths parser which is described in EPOCH maths parser. If the deck contains a “\” character then the rest of the line is ignored and the next line becomes a continuation of the current one. Also, the comment character is “#"; if the “#” character is used anywhere on a line then the remainder of that line is ignored. There are three input deck directive commands, which are:

• begin:block - Begin the block named block.
• end:block - Ends the block named block.
• import:filename - Includes another file (called filename) into the input deck at the point where the directive is encountered. The input deck parser reads the included file exactly as if the contents of the included file were pasted directly at the position of the import directive.

Each block must be surrounded by valid begin: and end: directives or the input deck will fail. There are currently fourteen valid blocks hard coded into the input deck reader, but it is possible for end users to extend the input deck. The fourteen built in blocks are:

• control - Contains information about the general code setup. See here
• boundaries - Contains information about the boundary conditions for this run. See here
• species - Contains information about the species of particles which are used in the code. Also details of how these are initialised. See here
• laser - Contains information about laser boundary sources. See here.
• fields - Contains information about the EM fields specified at the start of the simulation. See here.
• particles_from_file - Contains information about files used to load particle data. See here.
• window - Contains information about the moving window if the code is used in that fashion. See here.
• output - Contains information about when and how to dump output files. See here.
• output_global - Contains parameters which should be applied to all output blocks. See here.
• dist_fn - Contains information about distribution functions that should be calculated for output. See here.
• probe - Contains information about particle probes used for output. See here.
• collisions - Contains information about particle collisions. See here.
• qed - Contains information about QED pair production. See here.
• subset - Contains configuration for filters which can be used to modify the data to be output. See here.
• constant - Contains information about user defined constants and expressions. These are designed to simplify the initial condition setup. See here.