code: def cols_interact(static_col, fs_name, fs_order, fs_seas_name=None):
      """Returns all interactions between static_col and fourier series up to specified order
  
      :param static_col:
          column to interact with fourier series. can be an arbitrary patsy model term
          e.g. "ct1", "C(woy)", "is_weekend:Q('events_Christmas Day')"
      :param fs_name:
          column the fourier series is generated from, same as col_name in fourier_series_fcn
      :param fs_order: int
          generate interactions up to this order. must be <= order in fourier_series_fcn
      :param fs_seas_name: str
          same as seas_name in fourier_series_fcn
      :return: list[str]
          interaction terms to include in patsy model formula
      """
      interaction_columns = [None] * fs_order * 2
      for i in range(fs_order):
          k = i + 1
          sin_col_name = get_fourier_col_name(
              k, fs_name, function_name="sin", seas_name=fs_seas_name
          )
          cos_col_name = get_fourier_col_name(
              k, fs_name, function_name="cos", seas_name=fs_seas_name
          )
          interaction_columns[2 * i] = f"{static_col}:{sin_col_name}"
          interaction_columns[
              2 * i + 1
          ] = f"{static_col}:{cos_col_name}"
      return interaction_columns
  
file_path: greykite/greykite/algo/forecast/silverkite/forecast_simple_silverkite_helper.py
imports: import warnings
  import pandas
  from greykite.common import constants
  from greykite.common.constants import EVENT_DF_DATE_COL
  from greykite.common.constants import EVENT_DF_LABEL_COL
  from greykite.common.constants import EVENT_INDICATOR
  from greykite.common.features.timeseries_features import add_event_window_multi
  from greykite.common.features.timeseries_features import get_fourier_col_name
  from greykite.common.features.timeseries_features import get_holidays
  from greykite.common.python_utils import split_offset_str
label_desc: Use image node_id 1 for calling a global function with example usage: cols_interact(static_col, fs_name, fs_order, fs_seas_name) and returns: interaction_columns