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max-div

A versatile, high-performance solver for Maximum Diversity Problems — select the k most diverse of n items, under optional fairness constraints.

Highlights

  • ⚡ obtains near-optimal results within seconds-to-one-minute for problems up to n=200k

  • 🚀 leverages numba JIT-compilation for maximum speed without relying on pre-compiled binaries

  • ⚖️ natively supports flexible fairness constraints

    • uniquely supports constraints with overlapping sets & ranged counts

    • returns the least infeasible solution (with configurable weighted linear or quadratic penalties) when constraints conflict

    • provides proofs of (in)feasibility

  • 📐 uniquely supports 5+ distance metrics (L1, L2, L∞, Minkowski, cosine — or precomputed distances) and 4 diversity metrics (minimum, mean & geomean separation + mean pairwise distance) in any combination

  • 💾 computes item distances eagerly when memory allows (maximum speed), lazily when problem size requires (minimal memory usage)

  • 🤝 leverages multi-core CPUs with parallel workers in independent, cooperative or dynamically grouped configurations, without duplicating core problem data

Feature comparison of max-div against exact solvers and one-shot pickers: distance metrics, diversity objectives, constraint handling, time budgets and practical scale

The benchmarks compare max-div in depth with 10 other freely available solvers.

Installation

pip install max-div

Python 3.11+; free-threaded builds (3.14t) are supported and CI-tested (see the installation notes for the numba version they require).

Quick start

import numpy as np
from max_div import MaxDivProblem, MaxDivSolverBuilder, seconds

rng = np.random.default_rng(42)
vectors = rng.random((200, 5))               # 200 points in 5 dimensions

# select the 20 most diverse, improving for up to 5 seconds
problem = MaxDivProblem.new(vectors, k=20)
solution = MaxDivSolverBuilder(problem).with_preset(seconds(5)).build().solve()

print(solution.i_selected)                   # indices of the selected items

With fairness constraints

Require a minimum and/or maximum number of selected items from given subsets — useful for fair representation across groups. Groups may overlap, and infeasible constraints degrade gracefully to the least-infeasible selection rather than failing.

from max_div import Constraint

# require between 8 and 12 of the selected items from each half of the data
constraints = [
    Constraint(int_set=set(range(0, 100)),   min_count=8, max_count=12),
    Constraint(int_set=set(range(100, 200)), min_count=8, max_count=12),
]
problem = MaxDivProblem.new(vectors, k=20, constraints=constraints)

Documentation

Full documentation lives at max-div.readthedocs.io, including:

License

Licensed under the Apache License 2.0.

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