KLIEP                   Estimate Density Ratio p(x)/q(x) by KLIEP
                        (Kullback-Leibler Importance Estimation
                        Procedure)
RuLSIF                  Estimate alpha-Relative Density Ratio
                        p(x)/(alpha p(x) + (1-alpha) q(x)) by RuLSIF
                        (Relative unconstrained Least-Square Importance
                        Fitting)
densratio               Estimate Density Ratio p(x)/q(x)
squared_euclid_distance
                        Compute Squared Euclid Distance
uLSIF                   Estimate Density Ratio p(x)/q(x) by uLSIF
                        (unconstrained Least-Square Importance Fitting)
