Improve docstrings

Author: AlexAndorra

pymc/distributions/multivariate.py

@@ -2403,10 +2403,16 @@ class ZeroSumNormal(Distribution):
     By default, the last axis is constrained to sum to zero.
     See `zerosum_axes` kwarg for more details.
 
+    .. math:
+
+        ZSN(\sigma) = N(0, \sigma^2 (I - \tfrac{1}{n}J)
+        where $J_{ij} = 1$
+
     Parameters
     ----------
     sigma : tensor_like of float
-        Standard deviation (sigma > 0).
+        Scale parameter (sigma > 0).
+        It's actually the standard deviation of the underlying, unconstrained Normal distribution.
         Defaults to 1 if not specified.
         For now, ``sigma`` has to be a scalar, to ensure the zero-sum constraint.
     zerosum_axes: list or tuple of strings or integers

pymc/distributions/transforms.py

@@ -273,8 +273,7 @@ def bounds_fn(*rv_inputs):
 
 class ZeroSumTransform(RVTransform):
     """
-    Constrains the samples of a Normal distribution to sum to zero
-    along the user-provided ``zerosum_axes``.
+    Constrains any random samples to sum to zero along the user-provided ``zerosum_axes``.
     By default (``zerosum_axes=[-1]``), the sum-to-zero constraint is imposed
     on the last axis.
     """