code: public static void useFastMathExp(boolean useJafama) {
          if (useJafama) {
              register("binary:logistic", new RegLossObjLogistic_Jafama());
              register("multi:softprob", new SoftmaxMultiClassObjProb_Jafama());
  
          } else {
              register("binary:logistic", new RegLossObjLogistic());
              register("multi:softprob", new SoftmaxMultiClassObjProb());
          }
      }
docs: Uses Jafama's {@link FastMath#exp(double)} instead of {@link Math#exp(double)}.
  
  @param useJafama {@code true} if you want to use Jafama's {@link FastMath#exp(double)},
  or {@code false} if you don't want to use it but JDK's {@link Math#exp(double)}.