code: def _rdm(a, b):
      """Compute the ratio of norms, being careful about 0."""
      a_norm = np.linalg.norm(a, axis=0)
      b_norm = np.linalg.norm(b, axis=0)
      all_zero = (a_norm == 0) & (b_norm == 0)
      a_norm[all_zero] = 1.0
      b_norm[all_zero] = 1.0
      return a_norm / b_norm
  
imports: from itertools import product
  from pathlib import Path
  import numpy
  import pytest
  from numpy.testing import assert_allclose, assert_array_equal, assert_array_less
  from mne import convert_forward_solution, create_info, get_volume_labels_from_aseg, make_forward_solution, make_sphere_model, pick_info, pick_types, pick_types_forward, read_cov, read_dipole, read_evokeds, read_forward_solution, read_source_spaces, setup_volume_source_space, write_forward_solution
  from mne._fiff.constants import FIFF
  from mne.bem import make_bem_solution, read_bem_surfaces
  from mne.channels import make_standard_montage
  from mne.datasets import testing
  from mne.dipole import Dipole, fit_dipole
  from mne.forward import Forward, _do_forward_solution, use_coil_def
  from mne.forward._compute_forward import _magnetic_dipole_field_vec
  from mne.forward._make_forward import _create_meg_coils, make_forward_dipole
  from mne.forward.tests.test_forward import assert_forward_allclose
  from mne.io import read_info, read_raw_bti, read_raw_fif, read_raw_kit
  from mne.simulation import simulate_evoked
  from mne.source_estimate import VolSourceEstimate
  from mne.source_space._source_space import _compare_source_spaces, setup_source_space, write_source_spaces
  from mne.surface import _get_ico_surface
  from mne.transforms import Transform
  from mne.utils import catch_logging, requires_mne, requires_mne_mark, requires_openmeeg_mark, run_subprocess
label_desc: Use image node_id 2 for calling a global function with example usage: _rdm(a, b) and returns: unknown