config-spectrum 0.2.0

Configuration for the SPECTRUM software suite, enabling C++-native, compile-time full codebase parameterization.

Config-SPECTRUM

⚠️ DISCLAIMER: This project is currently under active pre-alpha development.

Config-SPECTRUM is a configuration assistant for SPECTRUM, facilitating C++-native compile-time configuration and parameter management.

Quick Start 🥚

The script is accessed via a command line entry point config-spectrum. Compile-time constants (parameters) may be set at the command line. The tool will also resolve a set of contingent defaults.

For example:

config-spectrum . -b Dipole -t Lorentz -d None

This will generate a config file with a default name (config.hh) in the current directory (.). This file will inject the default values for a Lorentz particle trajectory in a Dipole background, with no Diffusion model applied. The path argument is usually (.), but it can be modified. To change the name of the file, use the -o flag. As in:

config-spectrum ./my_path -b Dipole -t Lorentz -d None -o my_first_test

Now the generated file is in a local subdirectory, and is named my_first_test.config.hh. Config files are C++ header files. By convention, suffixed with config.hh instead of the usual .hh for a C++ header file.

For more information, use the help flag config-spectrum -h or config-spectrum --help.

Guide for Developers 💾

Except for the frontend in main.py, the implementation is in the submodule _impl, and should not need to be frequently modified.

The files config_parameters.py and config_physical.py in config-spectrum, and the file common/compiletime_lists.hh are the "source of truth" for all of SPECTRUM.

• compiletime_lists.hh. This file and included header files determine fundamental structure is exposed at compile-time. In particular, it determines what Backgrounds, Trajectories, and Diffusion classes are recognized by config-spectrum. The enum classes there may be edited when the source code is changed, to reflect changes to the SPECTRUM object model. For example, a new Background implemented in background_silly.hh / background_silly.cc can be registered in compiletime_lists.hh by adding Silly to the list of backgrounds.

• config_parameters.py. Contains a specification of all (hyper)parameters for the SPECTRUM test particle trajectory solver. It provides type information, possible ranges, a docstring, and a globally-defined fallthrough default value. Modifications of this file should be made in tandem with review and possible modifications of compiletime_lists.hh.

• config_physical.py. Contains

This leads to the following general heuristic for developers:

• Modifications of compiletime_lists.hh should be made in tandem with review and possible modifications of config_parameters.py, and vice versa.
• Modifications of config_physical.py can be freely made.

Whenever changes to either of the .py files are made, the .config.hh files that appear in /src/ need to be updated. This process has been automated. You only need to run:

config-spectrum . --mkdefaults

To proceed cautiously, it is recommended to run this first in testing mode:

config-spectrum . --mkdefaults --test

Setting default values in config_physical.py

The dict of dicts in conig_physical.py defines a "reasonable" default for the particular trajectory/background/diffusion type. This file is the unique location in the code where these default values are defined.

There is no inheritance mechanism, so each class repeats parameters defined in base classes. In some cases, this is indicated by commented-out dividers.

The dicts are used on an "as-needed" basis, so the definitions here are not brittle. config-spectrum will automatically check that every case has a default value.

The formatting of values of key-value pairs is performed by the value method in _impl/configdata.py. Each parameter (say, a floating point parameter) has its type resolved via the dictionaries in config.parameters.py. If this type is float, then the value is set as a float. If this type is string (for example, a file name), then this value is set as a string. Default values of strings can be set using an ordinary double-quote "..." string. If the type is type (a C++ type), then the type is set here inside of a double-quote string. Brace-initializer expressions can be used for default values.

The dict of dicts physical_defaults has the following structure:

physical_defaults = {
    'Background': ..., # dict of backgrounds
    'Trajectory': ..., # dict of trajectories
    'Diffusion': ..., # dict of diffusions
}

Notes

• It is not possible to do what config-spectrum does using compile-time language features of C++20, the version used by SPECTRUM. Therefore a custom-built solution is needed, and this is one possibility (among many) which takes advantage of the well-developed Python ecosystem. Experience with config-spectrum

Last Updated

Lucius Schoenbaum May 31, 2026