Corrected the mean for ZeroInflatedBinomial

Author: sagartomar

pymc/distributions/discrete.py

@@ -1462,7 +1462,7 @@ class ZeroInflatedBinomial(Discrete):
 
     ========  ==========================
     Support   :math:`x \in \mathbb{N}_0`
-    Mean      :math:`(1 - \psi) n p`
+    Mean      :math:`\psi n p`
     Variance  :math:`(1-\psi) n p [1 - p(1 - \psi n)].`
     ========  ==========================
 
@@ -1487,7 +1487,7 @@ def dist(cls, psi, n, p, *args, **kwargs):
         return super().dist([psi, n, p], *args, **kwargs)
 
     def get_moment(rv, size, psi, n, p):
-        mean = at.round((1 - psi) * n * p)
+        mean = at.round(psi * n * p)
         if not rv_size_is_none(size):
             mean = at.full(size, mean)
         return mean

pymc/tests/test_distributions_moments.py

@@ -553,11 +553,11 @@ def test_zero_inflated_poisson_moment(psi, theta, size, expected):
 @pytest.mark.parametrize(
     "psi, n, p, size, expected",
     [
-        (0.2, 7, 0.7, None, 4),
-        (0.2, 7, 0.3, 5, np.full(5, 2)),
-        (0.6, 25, np.arange(1, 6) / 10, None, np.arange(1, 6)),
+        (0.8, 7, 0.7, None, 4),
+        (0.8, 7, 0.3, 5, np.full(5, 2)),
+        (0.4, 25, np.arange(1, 6) / 10, None, np.arange(1, 6)),
         (
-            0.6,
+            0.4,
             25,
             np.arange(1, 6) / 10,
             (2, 5),