code: def covariance_factor(self):
      return 0.5 * self.silverman_factor()
  
imports: from __future__ import division, print_function, absolute_import
  from scipy import stats
  import numpy
  from numpy.testing import assert_almost_equal, assert_, assert_array_almost_equal, assert_array_almost_equal_nulp, assert_allclose
  import pytest
  from pytest import raises
label_desc: Use image node_id 1 for calling the _kde_subclass4 obj's underlying member method code with example usage: obj.covariance_factor() and returns: unknown