code: def _tril_indices(n):
      rows, cols = np.tril_indices(n)
      return rows * n + cols
  
imports: from __future__ import annotations
  from statsmodels.compat.python import Literal, lrange
  import warnings
  import numpy
  import pandas
  from pandas import DataFrame
  from pandas.tseries import offsets
  from pandas.tseries.frequencies import to_offset
  from statsmodels.tools.data import _is_recarray, _is_using_pandas
  from statsmodels.tools.sm_exceptions import ValueWarning
  from statsmodels.tools.typing import NDArray
  from statsmodels.tools.validation import array_like, bool_like, int_like, string_like
label_desc: Use image node_id 8 for calling a global function with example usage: _tril_indices(n) and returns: unknown