code: def _log_exp_var(data, est, prefix="    "):
      res = data - est
      var_exp = 1 - (
          (res * res.conj()).sum().real
          / (data * data.conj()).sum().real
      )
      var_exp *= 100
      logger.info(f"{prefix}Explained {var_exp:5.1f}% variance")
      return var_exp
  
imports: from copy import deepcopy
  from math import sqrt
  import numpy
  from scipy import linalg
  from scipy.stats import chi2
  from .._fiff.constants import FIFF
  from .._fiff.matrix import _read_named_matrix, _transpose_named_matrix, write_named_matrix
  from .._fiff.open import fiff_open
  from .._fiff.pick import channel_type, pick_channels, pick_info, pick_types
  from .._fiff.proj import _electrode_types, _needs_eeg_average_ref_proj, _read_proj, _write_proj, make_projector
  from .._fiff.tag import find_tag
  from .._fiff.tree import dir_tree_find
  from .._fiff.write import end_block, start_and_end_file, start_block, write_coord_trans, write_float, write_float_matrix, write_int, write_string
  from ..cov import Covariance, _read_cov, _write_cov, compute_whitener, prepare_noise_cov
  from ..epochs import BaseEpochs, EpochsArray
  from ..evoked import Evoked, EvokedArray
  from ..fixes import _safe_svd
  from ..forward import _read_forward_meas_info, _select_orient_forward, compute_depth_prior, compute_orient_prior, convert_forward_solution, is_fixed_orient
  from ..forward.forward import _triage_loose, write_forward_meas_info
  from ..html_templates import _get_html_template
  from ..io import BaseRaw
  from ..source_estimate import _get_src_type, _make_stc
  from ..source_space._source_space import _get_src_nn, _get_vertno, _read_source_spaces_from_tree, _write_source_spaces_to_fid, find_source_space_hemi, label_src_vertno_sel
  from ..surface import _normal_orth
  from ..time_frequency.tfr import _check_tfr_complex
  from ..transforms import _ensure_trans, transform_surface_to
  from ..utils import _check_compensation_grade, _check_depth, _check_fname, _check_option, _check_src_normal, _validate_type, _verbose_safe_false, check_fname, logger, repr_html, verbose, warn
  from ._eloreta import _compute_eloreta
label_desc: Use image node_id 14 for calling a global function with example usage: _log_exp_var(data, est, prefix) and returns: var_exp