code: def _bem_specify_els(bem, els, mults):
      """Set up for computing the solution at a set of EEG electrodes.
  
      Parameters
      ----------
      bem : instance of ConductorModel
          BEM information
      els : list of dict, len(n_EEG_sensors)
          List of EEG sensor information dicts
      mults: ndarray, shape (1, n_BEM_vertices)
          Multiplier for every vertex in BEM
  
      Returns
      -------
      sol : ndarray, shape (n_EEG_sensors, n_BEM_vertices)
          EEG solution
      """
      sol = np.zeros((len(els), bem["solution"].shape[1]))
      scalp = bem["surfs"][0]
  
      # Operate on all integration points for all electrodes (in MRI coords)
      rrs = np.concatenate(
          [
              apply_trans(bem["head_mri_t"]["trans"], el["rmag"])
              for el in els
          ],
          axis=0,
      )
      ws = np.concatenate([el["w"] for el in els])
      tri_weights, tri_idx = _project_onto_surface(rrs, scalp)
      tri_weights *= ws[:, np.newaxis]
      weights = np.matmul(
          tri_weights[:, np.newaxis],
          bem["solution"][scalp["tris"][tri_idx]],
      )[:, 0]
      # there are way more vertices than electrodes generally, so let's iterate
      # over the electrodes
      edges = np.concatenate(
          [[0], np.cumsum([len(el["w"]) for el in els])]
      )
      for ii, (start, stop) in enumerate(zip(edges[:-1], edges[1:])):
          sol[ii] = weights[start:stop].sum(0)
      sol *= mults
      return sol
  
imports: from copy import deepcopy
  import numpy
  from .._fiff.constants import FIFF
  from ..bem import _import_openmeeg, _make_openmeeg_geometry
  from ..fixes import bincount, jit
  from ..parallel import parallel_func
  from ..surface import _jit_cross, _project_onto_surface
  from ..transforms import apply_trans, invert_transform
  from ..utils import _check_option, _pl, fill_doc, logger, verbose, warn
label_desc: Use image node_id 7 for calling a global function with example usage: _bem_specify_els(bem, els, mults) and returns: sol