athelas (Astrophysical Transients with Hydrodynamics and Emission using a Lagrangian Arbitrary-order Scheme )

1D Lagrangian radiation-hydrodynamics solver written in C++

Athelas solves the 1D Lagrangian equation of non-relativistic radiation hydrodynamics using a nodal discontinuous Galerkin scheme. Key features:

• Two moment radiation transport with fully implicit integration and an IMEX treatment.
• Lagrangian hydrodynamics
• LTE Saha ionization
• A nickel decay network and heating
• Newtonian self gravity
• High order, conservative discontinuous Galerkin methods
• Spherical and flat Cartesian geometries
• Fully coupled IMEX time integration
• Artificially driven explosions
• A sophisticated package system to thread new physics into the timestepper

Work in progress docs are available.

Installation

athelas uses submodules to include dependencies. The best way to get the source is the following

git clone --recursive https://github.com/athelas-astro/athelas.git

Building

The easiest way to build is with cmake. From the root directory of athelas, run:

mkdir build && cd build
cmake ..
cmake --build . # or make -j

An experimental xmake build is also available:

xmake f
xmake build athelas
xmake run athelas -i inputs/sod.lua

Alongside xmake's debug, release, releasedbg, and profile modes, Athelas provides relwithdebinfo (CMake-style RelWithDebInfo) and perf (sampling profiles without -pg). The asan, tsan, ubsan, and lsan modes use xmake's corresponding sanitizer policies. allsan combines the compatible address, leak, and undefined-behavior sanitizers with debug settings; ThreadSanitizer must be run separately.

Dependencies built from submodules are cached under build/.packages/ and keyed on the submodule revision, so a bump rebuilds them. A dependency is cached as a unit, so that rebuild is a full one.

Running

To run athelas simply execute ./athelas -i ../inputs/sod.lua, for instance.

Tests

Regression tests live in test/regression. To run all test, run python run_regression_tests.py. Pass -e /path/to/athelas/executable to avoid rebuilding each test. To run a specific test, run python run_regression_tests.py --test test_sod -e /path/to/athelas/executable etc.

To build and run the unit tests with xmake:

xmake f --unit_tests=y
xmake test -g unit

The group filter runs the unit suite without invoking regression tests, even when both test options are enabled.

Regression tests are registered separately:

xmake f --regression_tests=y
xmake test -g regression
xmake test regression_tests/sod

When available, xmake runs the regression suite in the locked uv environment under scripts/python/athelas_tools. Otherwise, the active Python environment must provide the regression-test dependencies.

Kokkos

We use Kokkos for shared memory parallelism.

Sol

We use Sol for parsing input configuration using the Lua language. This means that Lua is required for running Athelas.

Code Style

We use clang format and ruff for code cleanliness. Rules are listed in .clang-format. The current version of clang-format used is 20.1.0. Simply call tools/bash/format.sh to format the .hpp and .cpp files.

Python code linting and formatting is done with ruff. Rules are listed in ruff.toml. To check all python in the current directory, you may ruff .. To format a given file according to ruff.toml, run ruff format file.py.

Checks for formatting are performed on each PR.

There is also a Git pre-commit hook available in scripts/hooks that will perform this formatting on a commit. You can enable this simply by

./scripts/hooks/install-hooks.sh

which will automatically symlink the hook into .git/hooks.

Dependencies

• Eigen (submodule)
• Kokkos (submodule)
• Sol (submodule)
• Lua
• HDF5

Contributors

Name	Handle	Affiliation
Brandon L. Barker	@AstroBarker	LANL