Let prob_cleanup raise exception if inaccurate.

Fixes #203.
nengo · Aug 27, 2018 · 2da500a · 2da500a
1 parent ed4a3ae
commit 2da500a
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diff --git a/nengo_spa/math.py b/nengo_spa/math.py
@@ -15,4 +15,8 @@ def prob_cleanup(similarity, dimensions, vocab_size):
 
     Requires SciPy.
     """
-    return CosineSimilarity(dimensions).cdf(similarity) ** vocab_size
+    p = CosineSimilarity(dimensions).cdf(similarity)
+    if similarity < 1. and p == 1.:
+        raise ArithmeticError(
+            "Insufficient floating point precision to compute value.")
+    return p ** vocab_size
diff --git a/nengo_spa/tests/test_math.py b/nengo_spa/tests/test_math.py
@@ -1,3 +1,4 @@
+import numpy as np
 import pytest
 
 from nengo_spa.math import prob_cleanup
@@ -13,3 +14,7 @@ def test_prob_cleanup(rng):
     assert 0.999 > prob_cleanup(0.4, 128, 1000) > 0.997
     assert 0.99 > prob_cleanup(0.4, 128, 10000) > 0.97
     assert 0.9 > prob_cleanup(0.4, 128, 100000) > 0.8
+    assert prob_cleanup(0.4, 128, np.inf) == 0.
+
+    with pytest.raises(ArithmeticError):
+        prob_cleanup(0.2, 2025, np.inf)