MABELab-RS/DETERMINISM.md

Determinism Policy

MabeLabRS emphasizes reproducibility of artificial life experiments.

Randomness

• Use rand_chacha::ChaCha8Rng (fast, reproducible).
• Seeds must be explicit and logged in experiment manifests.

Floating-point

• Default: f64.
• Avoid nondeterministic parallel reductions; when needed, gate behind the fast-math feature.
• Golden tests should tolerate ≤ 1e-12 relative error in float comparisons.

Collections

• Use BTreeMap/BTreeSet when deterministic ordering is required.
• Use indexmap::IndexMap/IndexSet for hash-backed structures that preserve insertion order.

Parallelism

• Sequential by default.
• rayon parallelism only behind parallel feature flag.
• Golden tests must run with --no-default-features to guarantee determinism.