docstr: Approximate derivative of the energy profile
  
  Returns the derivative of the estimated energy as a function of "time"
  (iterations) at the last iteration
code: def _get_energy_derivative(self):
      """Approximate derivative of the energy profile
  
      Returns the derivative of the estimated energy as a function of "time"
      (iterations) at the last iteration
      """
      n_iter = len(self.energy_list)
      if n_iter < self.energy_window:
          raise ValueError("Not enough data to fit the energy profile")
      x = range(self.energy_window)
      y = self.energy_list[(n_iter - self.energy_window) : n_iter]
      ss = sum(y)
      if not ss == 0:  # avoid division by zero
          ss = -ss if ss > 0 else ss
          y = [v / ss for v in y]
      der = self._approximate_derivative_direct(x, y)
      return der
  
imports: import logging
  import abc
  import numpy
  import numpy.linalg
  import nibabel
  from nibabel.streamlines import ArraySequence
  from dipy.align import vector_fields
  from dipy.align import floating
  from dipy.align import VerbosityLevels
  from dipy.align import Bunch
  from dipy.align.scalespace import ScaleSpace
label_desc: Use image node_id 11 for calling the SymmetricDiffeomorphicRegistration obj's underlying member method code with example usage: obj._get_energy_derivative() and returns: der