fix unbalance for binary classification

src/objective/binary_objective.hpp

@@ -47,8 +47,8 @@ public:
     label_weights_[1] = 1.0f;
     // if using unbalance, change the labels weight
     if (is_unbalance_) {
-      label_weights_[1] = 1.0f / cnt_positive;
-      label_weights_[0] = 1.0f / cnt_negative;
+      label_weights_[1] = 1.0f;
+      label_weights_[0] = static_cast<float>(cnt_positive) / cnt_negative;
     }
   }