code: public float predictSingle(FVec feat, boolean output_margin, int ntree_limit) {
          float pred = predictSingleRaw(feat, ntree_limit);
          if (!output_margin) {
              pred = obj.predTransform(pred);
          }
          return pred;
      }
docs: Generates a prediction for given feature vector.
  <p>
  This method only works when the model outputs single value.
  </p>
  
  @param feat          feature vector
  @param output_margin whether to only predict margin value instead of transformed prediction
  @param ntree_limit   limit the number of trees used in prediction
  @return prediction value