Method PredTransform

plugin/example/custom_obj.cc:59–65

    return "logloss";
  }
  void PredTransform(HostDeviceVector<float> *io_preds) const override {
    // transform margin value to probability.
    std::vector<float> &preds = io_preds->HostVector();
    for (auto& pred : preds) {
      pred = 1.0f / (1.0f + std::exp(-pred));
    }
  }
  void ProbToMargin(linalg::Vector<float>* base_score) const override {
    // transform probability to margin value
    auto h_intercept = base_score->HostView();