code: def _st(x, start_f, windows):
      """Compute ST based on Ali Moukadem MATLAB code (used in tests)."""
      from scipy.fft import fft, ifft
  
      n_samp = x.shape[-1]
      ST = np.empty(
          x.shape[:-1] + (len(windows), n_samp), dtype=np.complex128
      )
      # do the work
      Fx = fft(x)
      XF = np.concatenate([Fx, Fx], axis=-1)
      for i_f, window in enumerate(windows):
          f = start_f + i_f
          ST[..., i_f, :] = ifft(XF[..., f : f + n_samp] * window)
      return ST
  
file_path: mne-python/mne/time_frequency/_stockwell.py
imports: from copy import deepcopy
  import numpy
  from scipy.fft import fft, fftfreq, ifft
  from .._fiff.pick import _pick_data_channels, pick_info
  from ..parallel import parallel_func
  from ..utils import _validate_type, fill_doc, logger, verbose
  from .tfr import AverageTFR, _get_data
label_desc: Use image node_id 3 for calling a global function with example usage: _st(x, start_f, windows) and returns: ST