code: def _mom(self, k, dist, length, cache):
          
          return numpy.prod(dist.mom(k), 0)
docs: Moment generating function.
  
          Example:
              >>> print(chaospy.Iid(chaospy.Uniform(), 2).mom(
              ...     [[0, 0, 1], [0, 1, 1]]))
              [1.   0.5  0.25]