code: def evolution(self):
      if self._evol_kx is not None:
          return np.asarray(self._evol_kx)
      else:
          return None
  
imports: import abc
  import warnings
  import numpy
  import scipy.sparse
  import scipy.optimize
  from scipy.optimize import minimize
  from dipy.utils.optpkg import optional_package
label_desc: Use image node_id 8 for calling the Optimizer obj's underlying member method code with example usage: obj.evolution() and returns: np, None