code: def min_train_series_length(self) -> int:
      # LightGBM requires a minimum of 2 train samples, therefore the min_train_series_length should be one more than
      # for other regression models
      return max(
          3,
          -self.lags["target"][0] + self.output_chunk_length + 1
          if "target" in self.lags
          else self.output_chunk_length,
      )
  
file_path: darts/darts/models/forecasting/lgbm.py
imports: from typing import List, Optional, Sequence, Union
  import lightgbm
  import numpy
  from darts.logging import get_logger
  from darts.models.forecasting.regression_model import FUTURE_LAGS_TYPE, LAGS_TYPE, RegressionModelWithCategoricalCovariates, _LikelihoodMixin
  from darts.timeseries import TimeSeries
label_desc: Use image node_id 5 for calling the LightGBMModel obj's underlying member method code with example usage: obj.min_train_series_length() and returns: max