KO_evaluation           evaluate performance of KKO selection
generate_data           generate response from nonparametric additive
                        model
kko                     variable selection for additive model via KKO
rk_fit                  nonparametric additive model seleciton via
                        random kernel
rk_subsample            compute selection frequency of rk_fit on
                        subsamples
rk_tune                 tune random feature number for KKO.
