code: def _ems_diff(data0, data1):
      """Compute the default diff objective function."""
      return np.mean(data0, axis=0) - np.mean(data1, axis=0)
  
file_path: mne-python/mne/decoding/ems.py
imports: from collections import Counter
  import numpy
  from .._fiff.pick import _picks_to_idx, pick_info, pick_types
  from ..parallel import parallel_func
  from ..utils import logger, verbose
  from .base import _set_cv
  from .mixin import EstimatorMixin, TransformerMixin
label_desc: Use image node_id 2 for calling a global function with example usage: _ems_diff(data0, data1) and returns: unknown