There are three different versions of Ludi (i.e., Ludi_1, Ludi_2, Ludi_3) [61, 62, 69] . According to the Discovery Studio user manual, only the weight factors employed by Ludi_2 for each term are derived by fitting to experimentally determined binding affinities. In fact, all three versions were tested for enrichment rates of virtual screening against BACE-1 in our study, and we found that Ludi_1 outperforms the other two versions.