code: def compute_chpi_snr(
      raw,
      t_step_min=0.01,
      t_window="auto",
      ext_order=1,
      tmin=0,
      tmax=None,
      verbose=None,
  ):
      """Compute time-varying estimates of cHPI SNR.
  
      Parameters
      ----------
      raw : instance of Raw
          Raw data with cHPI information.
      t_step_min : float
          Minimum time step to use.
      %(t_window_chpi_t)s
      %(ext_order_chpi)s
      %(tmin_raw)s
      %(tmax_raw)s
      %(verbose)s
  
      Returns
      -------
      chpi_snrs : dict
          The time-varying cHPI SNR estimates, with entries "times", "freqs",
          "snr_mag", "power_mag", and "resid_mag" (and/or "snr_grad",
          "power_grad", and "resid_grad", depending on which channel types are
          present in ``raw``).
  
      See Also
      --------
      mne.chpi.compute_chpi_locs, mne.chpi.compute_chpi_amplitudes
  
      Notes
      -----
      .. versionadded:: 0.24
      """
      return _compute_chpi_amp_or_snr(
          raw,
          t_step_min,
          t_window,
          ext_order,
          tmin,
          tmax,
          verbose,
          snr=True,
      )
  
imports: import copy
  import itertools
  from functools import partial
  import numpy
  from scipy.linalg import orth
  from scipy.optimize import fmin_cobyla
  from scipy.spatial.distance import cdist
  from ._fiff.constants import FIFF
  from ._fiff.meas_info import Info, _simplify_info
  from ._fiff.pick import _picks_to_idx, pick_channels, pick_channels_regexp, pick_info, pick_types
  from ._fiff.proj import Projection, setup_proj
  from .channels.channels import _get_meg_system
  from .cov import compute_whitener, make_ad_hoc_cov
  from .dipole import _make_guesses
  from .event import find_events
  from .fixes import jit
  from .forward import _concatenate_coils, _create_meg_coils, _magnetic_dipole_field_vec
  from .io import BaseRaw
  from .io.ctf.trans import _make_ctf_coord_trans_set
  from .io.kit.constants import KIT
  from .io.kit.kit import RawKIT
  from .preprocessing.maxwell import _get_mf_picks_fix_mags, _prep_mf_coils, _regularize_out, _sss_basis
  from .transforms import _angle_between_quats, _fit_matched_points, _quat_to_affine, als_ras_trans, apply_trans, invert_transform, quat_to_rot, rot_to_quat
  from .utils import ProgressBar, _check_fname, _check_option, _on_missing, _pl, _validate_type, _verbose_safe_false, logger, use_log_level, verbose, warn
label_desc: Use image node_id 27 for calling a global function with example usage: compute_chpi_snr(raw, t_step_min, t_window, ext_order, tmin, tmax, verbose) and returns: _compute_chpi_amp_or_snr