Building from Source

monoprop has one supported from-source build workflow:

the Python bindings — the nanobind extension behind import monoprop, built with scikit-build-core and driven by uv (or pip);
the C++ unit tests — built within the same uv (or pip) invocation.

MPI is off by default in every build path; you enable it explicitly. The mechanism differs by build:

Build	Enable MPI with
Python bindings and C++ tests (scikit-build / `uv` / `pip`)	`--config-settings=cmake.define.monoprop_ENABLE_MPI=ON` (or export `SKBUILD_CMAKE_ARGS="-Dmonoprop_ENABLE_MPI=ON"`)

The prebuilt wheels published to PyPI (pip install monoprop) are also built without MPI, so a from-source build is required for multi-rank runs.

Prerequisites

a C++23-compliant compiler; on Linux the minimum supported versions are GCC 14 and Clang 18
CMake and Ninja
Python 3.11 or newer and the uv package manager (for the bindings)
an MPI implementation such as Open MPI (only for MPI builds)
hwloc (version 2.9+) and pkg-config (required so CMake can locate hwloc)

The repository ships a DevContainer with all of the above pre-configured; opening the folder in VS Code and rebuilding the container is the quickest route to a working environment.

Building with Nix

The repository is also a Nix flake:

Command	What it gives you
`nix develop`	a shell with every prerequisite above, plus `uv`, `just` and Node.js
`nix build .#monoprop`	the Python package, built without MPI
`nix build .#monoprop-mpi`	the same package with `monoprop_ENABLE_MPI=ON`
`nix run`	a Python interpreter with `monoprop` importable

Inside nix develop the uv sync and just workflows below apply unchanged. The shell sets two variables that only matter on NixOS: UV_PYTHON_PREFERENCE=only-system, because uv's managed interpreters expect a loader NixOS does not provide, and LD_LIBRARY_PATH, so that manylinux wheels can resolve libstdc++.

The packaged build deviates from the uv build in three places, all in nix/monoprop.nix:

the C++ unit tests are disabled, because they resolve msgpack-cxx through a git fetch that the build sandbox denies — build them from the dev shell instead;
monoprop_ENABLE_ARCH_FLAGS is off, since a store path may be substituted onto a machine other than the one that built it; pass .override { enableArchFlags = true; } for a native build;
the version is pinned, because setuptools-scm cannot read git metadata inside the sandbox; bump it alongside the release tag.

Building the Python bindings

uv creates a virtual environment, installs the Python dependencies, and compiles the nanobind extension in editable mode. Re-run the sync command whenever the dependency graph or the C++ sources change.

Without MPI (default)

uv sync --all-extras -v

This produces a single-process build with no MPI dependency.

With MPI

Pass a config-settings override to enable MPI:

uv sync --all-extras -v \
    --config-settings=cmake.define.monoprop_ENABLE_MPI=ON

The same override works with pip when installing from a checkout:

pip install . --config-settings=cmake.define.monoprop_ENABLE_MPI=ON

Verify the install

uv run python -c "import monoprop as mp; print(mp.__version__)"

Running the bindings

A serial run is just a normal Python invocation:

uv run python your_script.py

For a multi-rank run, launch the same script under mpiexec (requires an MPI build) and pass comm=MPI.COMM_WORLD to the simulator:

mpiexec -n 8 uv run python your_script.py

See Parallelism and distribution for the communicator options and the operator-partitioning controls.

Building the C++ unit tests

The supported C++ workflow reuses the build tree produced by uv sync. Do not run cmake --preset ... to configure this project directly: the top-level CMake configuration expects scikit-build-core to provide Python, nanobind, and related cache variables. Instead, first create the tree with uv sync, then invoke ctest directly to run the C++ unit tests.

Release tree

uv sync --all-extras -v
ctest --test-dir build/editable/Release

This uses the scikit-build-core Release tree at build/editable/Release and runs bin/monoprop_unit_tests.x there.

Debug tree

uv sync --all-extras -v --config-settings=cmake.build-type=Debug
ctest --test-dir build/editable/Debug

Use just test-wide for the 64-bit monoprop_WIDE_TERM_INDEX configuration.
Use just code-coverage for the coverage build.
Use ctest --test-dir build/editable/Release -L serial or -L mpi-2 to filter the discovered C++ test set.