.param Files

Section author: Axel Huebl

Parameter files, *.param placed in include/picongpu/simulation_defines/param/ are used to set all compile-time options for a PIConGPU simulation. This includes most fundamental options such as numerical solvers, floating precision, memory usage due to attributes and super-cell based algorithms, density profiles, initial conditions etc.

Rationale

High-performance hardware comes with a lot of restrictions on how to use it, mainly memory, control flow and register limits. In order to create an efficient simulation, PIConGPU compiles to exactly the numerical solvers (kernels) and physical attributes (fields, species) for the setup you need to run, which will furthermore be specialized for a specific hardware.

This comes at a small cost: when one of those settings is changed, you need to recompile. Nevertheless, wasting about 5 minutes compiling on a single node is nothing compared to the time you save at scale!

All options that are less or non-critical for runtime performance, such as specific ranges observables in plugins or how many nodes shall be used, can be set in run time configuration files (*.cfg) and do not need a recompile when changed.

Files and Their Usage

If you use our pic-configure script wrappers, you do not need to set all available parameter files since we will add the missing ones with sane defaults. Those defaults are:

  • a standard, single-precision, well normalized PIC cycle suitable for relativistic plasmas
  • no external forces (no laser, no initial density profile, no background fields, etc.)