Summary

If the optional adaptive-triangulation package (>= 0.2.1) is installed, its Rust Triangulation is now used automatically as a drop-in replacement for the pure-Python implementation, making LearnerND significantly faster (~3.7x end-to-end on ring_of_fire, and ~7x faster than Learner2D at 5k points).

pip install "adaptive[rust]"

How it works

• New adaptive/learner/triangulation_backend.py selects the backend at import time: the Rust package when importable and >= 0.2.1, otherwise the pure-Python implementation. learnerND.py, learner1D.py, and learner2D.py import Triangulation / circumsphere / point_in_simplex / simplex_volume_in_embedding from it.
• Per-learner control: LearnerND(..., triangulation_backend="auto" | "python" | "rust"), or pass a Triangulation-compatible class directly. "rust" raises a helpful ImportError when the package is missing or too old.
• Global override: ADAPTIVE_TRIANGULATION_BACKEND=auto|python|rust environment variable.
• The pure-Python adaptive.learner.triangulation names are deliberately never shadowed, so existing pickles that reference adaptive.learner.triangulation.Triangulation by qualified name keep loading, and old LearnerND pickles fall back to a class-level _triangulation_class attribute.

Bug fix

_pop_highest_existing_simplex evaluated None in self._subtriangulations[simplex].simplices for stale queue entries. Python sets return False; the Rust proxy raises TypeError. Now guarded with subsimplex is not None.

Testing

• 8 new tests in adaptive/tests/unit/test_triangulation_backend.py covering auto-selection, env-var override, constructor argument, custom class pass-through, and error paths.
• Full suite passes with the Rust backend absent (282 passed) and with Rust 0.2.1 active, except 7 curvature-loss tests that hit a known remaining divergence in adaptive-triangulation (simplex_volume_in_embedding raises on collinear input where the reference returns 0.0) - to be fixed there; only a _MIN_RUST_VERSION bump is needed here afterwards.

Note: the rust extra is not added to the test/dev extras yet; consider adding a CI job with the Rust backend once the degenerate-simplex fix is released.