docstr: set zero displacements at the boundary
  
  Parameters
  ----------
  step : array, ndim 2 or 3
      displacements field
  
  Returns
  -------
  step : array, ndim 2 or 3
      displacements field
code: def __set_no_boundary_displacement(self, step):
      """set zero displacements at the boundary
  
      Parameters
      ----------
      step : array, ndim 2 or 3
          displacements field
  
      Returns
      -------
      step : array, ndim 2 or 3
          displacements field
      """
      step[0, ...] = 0
      step[:, 0, ...] = 0
      step[-1, ...] = 0
      step[:, -1, ...] = 0
      if self.dim == 3:
          step[:, :, 0, ...] = 0
          step[:, :, -1, ...] = 0
      return step
  
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 8 for calling the SymmetricDiffeomorphicRegistration obj's underlying member method code with example usage: obj.__set_no_boundary_displacement(step) and returns: step