code: def hess(self, x):
      self.nhev += 1
      return 4 * np.eye(2)
  
imports: from __future__ import division, print_function, absolute_import
  import numpy
  from numpy.testing import TestCase, assert_array_almost_equal, assert_array_equal, assert_
  from scipy.sparse import csr_matrix
  from scipy.sparse.linalg import LinearOperator
  from scipy.optimize._differentiable_functions import ScalarFunction, VectorFunction, LinearVectorFunction, IdentityVectorFunction
label_desc: Use image node_id 4 for calling the ExScalarFunction obj's underlying member method code with example usage: obj.hess(x) and returns: unknown