feat(ga): generation summary stats (median/max/p90/entropy)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/multi_swarm/ga/summary.py

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+from __future__ import annotations
+
+import math
+
+import numpy as np
+
+
+def generation_summary(fitnesses: list[float], n_bins: int = 10) -> dict[str, float]:
+    arr = np.asarray(fitnesses, dtype=float)
+    if arr.size == 0:
+        return {"median": 0.0, "max": 0.0, "p90": 0.0, "entropy": 0.0}
+    median = float(np.median(arr))
+    fmax = float(np.max(arr))
+    p90 = float(np.percentile(arr, 90))
+
+    if fmax > 0:
+        normalized = arr / fmax
+    else:
+        normalized = arr
+
+    hist, _ = np.histogram(normalized, bins=n_bins, range=(0.0, 1.0))
+    total = hist.sum()
+    probs = hist / total if total > 0 else hist
+    entropy = float(-sum(p * math.log(p) for p in probs if p > 0))
+
+    return {"median": median, "max": fmax, "p90": p90, "entropy": entropy}

tests/unit/test_ga_summary.py

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+import math
+
+import pytest
+
+from multi_swarm.ga.summary import generation_summary
+
+
+def test_summary_basic_stats():
+    fitnesses = [0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9]
+    s = generation_summary(fitnesses, n_bins=5)
+    assert s["median"] == pytest.approx(0.45, abs=0.05)
+    assert s["max"] == pytest.approx(0.9)
+    assert 0.0 <= s["entropy"] <= math.log(5) + 0.01
+
+
+def test_summary_uniform_high_entropy():
+    fitnesses = [0.1 * i for i in range(20)]
+    s_uniform = generation_summary(fitnesses, n_bins=5)
+    s_concentrated = generation_summary([0.5] * 20, n_bins=5)
+    assert s_uniform["entropy"] > s_concentrated["entropy"]
+
+
+def test_summary_p90():
+    fitnesses = list(range(100))
+    s = generation_summary([float(x) for x in fitnesses], n_bins=10)
+    assert 88.0 <= s["p90"] <= 91.0