code: public static DiscreteFactor normalizeVariance(DiscreteFactor featureFactor, int featureVariableNum) {
      DiscreteFactor variance = getVariances(featureFactor, featureVariableNum);
      DiscreteFactor stdDev = new TableFactor(variance.getVars(), variance.getWeights().elementwiseSqrt());
  
      return featureFactor.product(stdDev.inverse());
    }
docs: Computes the empirical variance of the features in {@code featureFactor}
  and normalizes each feature such that its empirical variance is 1.
  
  @param featureFactor
  @param featureVariableNum
  @return