code: public static DiscreteFactor getVariances(DiscreteFactor featureFactor, int featureVariableNum) {
      return getVariances(Arrays.asList(featureFactor), featureVariableNum);
    }
docs: Gets the variance of the values of each assignment to
  {@code featureVariableNum} in {@code featureFactor}.
  
  @param featureFactor
  @param featureVariableNum
  @return