heuropt/CHANGELOG.md

Changelog

All notable changes to this project will be documented in this file.

The format is based on Keep a Changelog, and this project adheres to Semantic Versioning.

Unreleased

Added

• Decision tree update in README to cover all v0.3.0 algorithms, with a new top-level branch on "is each evaluation expensive?" so BayesianOpt / Tpe / Hyperband have a clear home.
• Comparison results snapshot at examples/compare-results.md — reference output of the harness across 7 benchmark problems and ~20 algorithms, captured after v0.3.0 landed.
• Instruction-count benchmarks via gungraun (the Rust 2026 rename of iai-callgrind) at benches/hot_paths.rs. Covers non_dominated_sort, crowding_distance, hypervolume_2d, hypervolume_nd (HSO), and one-generation costs of NSGA-II and CMA-ES, plus a short-run bench for every algorithm. Stable across machines via callgrind.
• Property-based test suite expansion: tests/properties.rs (Pareto-comparison antisymmetry, partitioning, operator bounds), tests/algorithm_properties.rs (per-algorithm determinism + population-size invariants — 32 tests, one per algorithm), tests/operator_properties.rs (every Variation / Initializer / Repair impl), tests/metric_properties.rs (HV / spacing invariants), and tests/numerical_stability.rs (empty / singleton / duplicate / flat-fitness / zero-width-bounds populations).
• Coverage-guided fuzz harness at fuzz/ (cargo-fuzz + libFuzzer). Eight targets covering pareto_compare, non_dominated_sort, hypervolume_2d, ParetoArchive, crowding_distance, spacing, SBX/PolyMut, and the Repair operators. Runs in CI for a short soak per PR; longer runs locally via cargo +nightly fuzz run <target>.
• cargo-mutants config at .cargo/mutants.toml for advisory mutation testing. Not gated in CI; run with cargo mutants to surface tests that don't actually check the behavior they look like they do.
• GitHub Actions CI at .github/workflows/ci.yml with fmt / clippy / test (4-feature matrix) / doc / MSRV / fuzz-smoke jobs, all gated on -D warnings.

Fixed

• pareto::sort::non_dominated_sort previously dropped indices when the dominance graph contained a cycle (which arises when objectives contain NaN — pareto_compare becomes intransitive). Fuzzing the partition invariant surfaced the bug; orphans now go into a final residual front.
• operators::repair::ProjectToSimplex could silently return the all-zero vector when the input vector's magnitude dwarfed total (the standard Duchi/Held-Wolfe τ computation lost precision and τ ≈ max(x), so max(x_i - τ, 0) rounded to zero everywhere). Detected by the clamp_to_bounds fuzzer; now falls through to a degenerate "all mass on argmax" projection above a 1e15 magnitude ratio, and is robust to floating-point precision loss in the algorithm's inner loop.

0.3.0 — 2026-05-05

Theme: filling heuropt's expensive-evaluation, gradient-free, and constraint-handling gaps. No breaking changes to the v0.2.0 public API.

Added

New algorithms (9)

Sample-efficient / surrogate-based:

• BayesianOpt — Gaussian-process Bayesian Optimization with Expected Improvement acquisition. heuropt's first sample-efficient algorithm: targets the 50–500 evaluation regime.
• Tpe — Bergstra et al. 2011 Tree-structured Parzen Estimator (workhorse of Hyperopt and Optuna). KDE-based surrogate; cheaper per-step than BO and more robust without hyperparameter tuning.

Classical and modern evolution strategies:

• OnePlusOneEs — Rechenberg 1973 (1+1)-ES with the one-fifth success rule. Smallest possible self-adapting evolution strategy.
• IpopCmaEs — Auger & Hansen 2005 increasing-population CMA-ES with restart. Specifically fixes vanilla CMA-ES's known weakness on multimodal problems.
• SeparableNes — Wierstra et al. 2008/2014 Natural Evolution Strategy with diagonal covariance (sNES). Different theoretical foundation than CMA-ES; cheaper per-step at the cost of being unable to model rotated landscapes.

Direct search:

• NelderMead — Nelder & Mead 1965 simplex method. Classical gradient- free local optimizer; superb on low-dim smooth problems (Rosenbrock 5-D: f = 0 exactly).

Multi-fidelity:

• Hyperband — Li et al. 2017 multi-fidelity hyperparameter optimizer built on Successive Halving. Operates on a new PartialProblem trait so configurations can be evaluated at adjustable fidelity budgets.

New operators

• LevyMutation — heavy-tailed Lévy-flight mutation via Mantegna's algorithm. The actual algorithmic contribution from Cuckoo Search packaged as a reusable Variation operator.

New traits + impls

• PartialProblem — multi-fidelity problem contract: evaluate_at_budget(decision, budget) -> Evaluation. Used by Hyperband. Intentionally not a sub-trait of Problem.
• Repair<D> — in-place projection trait for restoring decisions to feasibility. Pair with Variation operators to get bounds-aware variants. Provided impls:
  • ClampToBounds for Vec<f64> per-axis clamping
  • ProjectToSimplex for L1-budget / probability-simplex projection

New selection helpers

• stochastic_ranking_select — Runarsson & Yao 2000 stochastic ranking. Better than strict feasibility-first tournament selection on heavily-constrained problems.

Internal helpers

• internal::cholesky — Cholesky factorization + triangular solves for SPD matrices, used by the GP posterior in BayesianOpt.

Changed

• CmaEsConfig gained initial_mean: Option<Vec<f64>>. None preserves the existing midpoint-of-bounds default; IpopCmaEs sets it to inject restart diversity without shrinking the search box.

0.2.0 — 2026-05-05

A substantial expansion of the algorithm catalog (21 new algorithms), five new operators, an n-D hypervolume utility, an algorithm-selection guide in the README, and a multi-seed comparison harness covering seven benchmark problems. No breaking changes to the v0.1.0 public API.

Added

New algorithms

Single-objective:

• HillClimber — simplest greedy local search.
• SimulatedAnnealing — Kirkpatrick et al. 1983, generic over decision type.
• GeneticAlgorithm — generational SO GA with tournament selection + elitism.
• ParticleSwarm — Eberhart & Kennedy 1995 PSO for Vec<f64>.
• CmaEs — Hansen & Ostermeier 2001 covariance-matrix adaptation.
• TabuSearch — Glover 1986, with a user-supplied neighbor generator.
• AntColonyTsp — Dorigo Ant System for permutation problems.
• Umda — Mühlenbein 1997 univariate marginal-distribution EDA for Vec<bool>.
• Tlbo — Rao 2011 Teaching-Learning-Based Optimization (parameter-free).

Multi-objective:

• Mopso — Coello, Pulido & Lechuga 2004 multi-objective PSO.
• Ibea — Zitzler & Künzli 2004 indicator-based EA.
• SmsEmoa — Beume, Naujoks & Emmerich 2007 S-metric selection EMOA.
• Hype — Bader & Zitzler 2011 Hypervolume Estimation Algorithm.
• Rvea — Cheng et al. 2016 Reference Vector-guided EA.
• PesaII — Corne et al. 2001 Pareto Envelope-based Selection II.
• EpsilonMoea — Deb, Mohan & Mishra 2003 ε-dominance MOEA.
• AgeMoea — Panichella 2019 Adaptive Geometry Estimation MOEA.
• Grea — Yang et al. 2013 Grid-based EA.
• Knea — Zhang, Tian & Jin 2015 Knee point-driven EA.

New operators

• BoundedGaussianMutation — Gaussian noise + per-axis clamping.
• SimulatedBinaryCrossover (SBX) — Deb & Agrawal 1995 canonical real-valued crossover.
• PolynomialMutation — Deb's polynomial mutation, the standard NSGA-II pair to SBX.
• CompositeVariation — pipeline two Variation operators (typically crossover → mutation).
• LevyMutation — heavy-tailed Lévy-flight mutation via Mantegna's algorithm.

New metrics / utilities

• hypervolume_nd — exact N-dimensional dominated hypervolume via the Hypervolume-by-Slicing-Objectives (HSO) algorithm, plus an internal Jacobi symmetric eigendecomposition helper used by CMA-ES.

New examples

• compare — multi-seed comparison harness running every applicable algorithm across ZDT1, ZDT3, DTLZ1, DTLZ2 (multi/many-objective) and Rastrigin, Rosenbrock, Ackley (single-objective). Reports hypervolume, spacing, mean L2/dist, front size, and wall-clock ms.
• benchmarks — canonical reference runs of NSGA-II on ZDT1 and DE on Rastrigin.
• jiggly_tuning — real-world 4-objective NSGA-III firmware tuning for the jiggly USB-mouse-jiggler, with an a-posteriori weighted-decision step that picks one recommendation off the Pareto front.

New optional feature

• parallel — rayon-backed parallel population evaluation in RandomSearch, Nsga2, DifferentialEvolution, Spea2, Ibea, Mopso, and most other algorithms with batchable inner loops. Seeded runs stay bit-identical to serial mode.

Documentation

• README gained an explanatory algorithm-selection decision tree that walks newcomers through choosing an optimizer, defining the terminology (multi-objective, Pareto front, dominance, multimodality, evaluation cost) as it goes.

Changed

• Minimum supported Rust version remains 1.85 (edition 2024).
• Algorithm impls now require P: Sync and P::Decision: Send so the same impl serves both parallel and serial feature builds. Any Problem / decision type without exotic interior mutability already satisfies these.

0.1.0 — 2026-05-04

Initial release.

Core types and traits

• Direction, Objective, ObjectiveSpace (with as_minimization direction conversion).
• Evaluation with feasibility (constraint_violation <= 0.0).
• Candidate<D>, Population<D>, OptimizationResult<D>.
• type Rng = rand::rngs::StdRng and rng_from_seed so no public trait is generic over the RNG.
• Problem, Optimizer<P>, Initializer<D>, Variation<D>.

Pareto utilities

• pareto_compare, pareto_front, best_candidate, non_dominated_sort (Deb fast non-dominated sort), crowding_distance, ParetoArchive<D>, das_dennis (structured reference points for NSGA-III and MOEA/D).

Operators

• Real: RealBounds, GaussianMutation, BoundedGaussianMutation, SimulatedBinaryCrossover (SBX), PolynomialMutation.
• Binary: BitFlipMutation.
• Permutation: SwapMutation.
• CompositeVariation pipeline (typically crossover → mutation).

Selection helpers

• select_random, tournament_select_single_objective.

Reference algorithms

• RandomSearch — sample-evaluate-keep baseline.
• Paes — small (1+1) Pareto Archived Evolution Strategy.
• Nsga2 — canonical Pareto-based EA with crowding distance.
• Nsga3 — many-objective NSGA-III with reference-point niching.
• Spea2 — Strength Pareto Evolutionary Algorithm 2.
• Moead — decomposition-based MOEA/D with the Tchebycheff scalar.
• DifferentialEvolution — single-objective DE/rand/1/bin.

Metrics

• spacing (Schott), hypervolume_2d (exact 2-D dominated hypervolume).

Examples

• random_search, toy_nsga2, custom_optimizer — minimum-viable walkthroughs.
• benchmarks — ZDT1 and Rastrigin reference runs.
• compare — multi-seed comparison harness running every applicable algorithm on ZDT1 (2-obj), DTLZ2 (3-obj), and Rastrigin (single-obj), reporting hypervolume, spacing, mean L2, front size, and wall time.
• jiggly_tuning — 4-objective NSGA-III tuning of the jiggly USB-mouse-jiggler firmware with an a-posteriori weighted-decision step that picks one recommendation off the Pareto front.

Optional features

• serde — Serialize / Deserialize derives on the core data types.
• parallel — rayon-backed parallel population evaluation in RandomSearch, Nsga2, and DifferentialEvolution. Seeded runs stay bit-identical to serial mode.