JF Tools

Collection of small useful helper tools for Python by Johannes Feist.

Short Iterative Lanczos Backend Selection

The jftools.short_iterative_lanczos solver now supports backend auto-dispatch for static Hamiltonians:

• cython when the Cython extension is built and importable.
• python for callable Hamiltonians and unsupported formats.

Select backend behavior with the backend function argument:

• auto (default): choose the best available backend.
• python: force the original Python implementation.
• cython: force Cython backend (requires compiled extension).

Example:

prop = jftools.short_iterative_lanczos.lanczos_timeprop(H, maxsteps=14, target_convg=1e-12, backend="cython")

Build Cython Extension

The Cython implementation is in jftools/short_iterative_lanczos_cython.pyx.

It is built automatically during normal installation via meson-python.

Recommended (uv-only) workflow:

uv sync --group dev
uv run python -m pip install -e . --no-build-isolation

For a non-editable local install through uv:

uv run python -m pip install .

After building, auto prefers cython.

QuTiP Compatibility

Short iterative Lanczos targets modern QuTiP (5.x):

• QuTiP Hamiltonians are converted through H.data.as_scipy() when available.
• QuTiP state outputs preserve dims and state shape.

Publishing

Releases are intended to be published through GitHub Actions rather than from a local machine.

Before publishing a new version:

1. Update the version in meson.build (the single source of truth; pyproject.toml picks it up automatically).
2. Commit and push the version bump.
3. Optionally run the Test release (TestPyPI) workflow to verify the full wheel matrix before publishing.
4. Create a GitHub Release or run the Publish workflow manually.

The publish workflow builds:

• wheels for CPython 3.12, 3.13, and 3.14,
• Linux x86_64 and aarch64,
• macOS x86_64 and arm64,
• Windows AMD64,
• plus an sdist.

For a dry run against TestPyPI, use the Test release (TestPyPI) workflow.

For a local packaging sanity check on your current machine only:

uv build