Merge branch 'pr/4725'

Reviewed at #4725
scipy · Apr 14, 2015 · 4f65e8e · 4f65e8e
2 parents c0f54db + a7ded12
commit 4f65e8e
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diff --git a/scipy/stats/_continuous_distns.py b/scipy/stats/_continuous_distns.py
@@ -2039,7 +2039,8 @@ def _ppf(self, q, a, c):
         return where(cond > 0, val1**ic, val2**ic)
 
     def _munp(self, n, a, c):
-        return special.gamma(a+n*1.0/c) / special.gamma(a)
+        # Pochhammer symbol: poch(a,n) = gamma(a+n)/gamma(a)
+        return special.poch(a, n*1.0/c)
 
     def _entropy(self, a, c):
         val = special.psi(a)

diff --git a/scipy/stats/tests/test_distributions.py b/scipy/stats/tests/test_distributions.py
@@ -1858,6 +1858,12 @@ def test_gengamma_edge():
     p = stats.gengamma.pdf(0, 1, 1)
     assert_equal(p, 1.0)
 
+    # Regression tests for gh-4724.
+    p = stats.gengamma._munp(-2, 200, 1.)
+    assert_almost_equal(p, 1./199/198)
+
+    p = stats.gengamma._munp(-2, 10, 1.)
+    assert_almost_equal(p, 1./9/8)
 
 def test_ksone_fit_freeze():
     # Regression test for ticket #1638.