code: def _check_is_univariate(y, var_name="input"):
      """Check if series is univariate."""
      if isinstance(y, pd.DataFrame):
          nvars = y.shape[1]
          if nvars > 1:
              raise ValueError(
                  f"{var_name} must be univariate, but found {nvars} variables."
              )
      if isinstance(y, np.ndarray) and y.ndim > 1 and y.shape[1] > 1:
          raise ValueError(
              f"{var_name} must be univariate, but found np.ndarray with more than "
              "one column"
          )
  
file_path: sktime/sktime/utils/validation/series.py
imports: from typing import Union
  import numpy
  import pandas
label_desc: Use image node_id 5 for calling a global function with example usage: _check_is_univariate(y, var_name) without return types