Method Train

src/treelearner/serial_tree_learner.cpp:173–237

}

Tree* SerialTreeLearner::Train(const score_t* gradients, const score_t *hessians, bool is_constant_hessian, const Json& forced_split_json) {
  gradients_ = gradients;
  hessians_ = hessians;
  is_constant_hessian_ = is_constant_hessian;
  #ifdef TIMETAG
  auto start_time = std::chrono::steady_clock::now();
  #endif
  // some initial works before training
  BeforeTrain();

  #ifdef TIMETAG
  init_train_time += std::chrono::steady_clock::now() - start_time;
  #endif

  auto tree = std::unique_ptr<Tree>(new Tree(config_->num_leaves));
  // root leaf
  int left_leaf = 0;
  int cur_depth = 1;
  // only root leaf can be splitted on first time
  int right_leaf = -1;

  int init_splits = 0;
  bool aborted_last_force_split = false;
  if (!forced_split_json.is_null()) {
    init_splits = ForceSplits(tree.get(), forced_split_json, &left_leaf,
                              &right_leaf, &cur_depth, &aborted_last_force_split);
  }

  for (int split = init_splits; split < config_->num_leaves - 1; ++split) {
    #ifdef TIMETAG
    start_time = std::chrono::steady_clock::now();
    #endif
    // some initial works before finding best split
    if (!aborted_last_force_split && BeforeFindBestSplit(tree.get(), left_leaf, right_leaf)) {
      #ifdef TIMETAG
      init_split_time += std::chrono::steady_clock::now() - start_time;
      #endif
      // find best threshold for every feature
      FindBestSplits();
    } else if (aborted_last_force_split) {
      aborted_last_force_split = false;
    }

    // Get a leaf with max split gain
    int best_leaf = static_cast<int>(ArrayArgs<SplitInfo>::ArgMax(best_split_per_leaf_));
    // Get split information for best leaf
    const SplitInfo& best_leaf_SplitInfo = best_split_per_leaf_[best_leaf];
    // cannot split, quit
    if (best_leaf_SplitInfo.gain <= 0.0) {
      Log::Warning("No further splits with positive gain, best gain: %f", best_leaf_SplitInfo.gain);
      break;
    }
    #ifdef TIMETAG
    start_time = std::chrono::steady_clock::now();
    #endif
    // split tree with best leaf
    Split(tree.get(), best_leaf, &left_leaf, &right_leaf);
    #ifdef TIMETAG