001d8c4023
* correct CalcDCG in rank_metric.cc DCG use log base-2, however `std::log` returns log base-e. * correct CalcDCG in rank_obj.cc DCG use log base-2, however `std::log` returns log base-e. * use std::log2 instead of std::log make it more elegant * use std::log2 instead of std::log make it more elegant