docstr: Try to interpret `obj` as a matrix
  
  Some operations are performed faster if we know in advance if a matrix
  is the identity (so we can skip the actual matrix-vector
  multiplication). This function returns None if the given object
  is None or the 'identity' string. It returns the same object if it is
  a numpy array. It raises an exception otherwise.
  
  Parameters
  ----------
  obj : object
      any object
  
  Returns
  -------
  obj : object
      the same object given as argument if `obj` is None or a numpy
      array. None if `obj` is the 'identity' string.
code: def interpret_matrix(self, obj):
      """Try to interpret `obj` as a matrix
  
      Some operations are performed faster if we know in advance if a matrix
      is the identity (so we can skip the actual matrix-vector
      multiplication). This function returns None if the given object
      is None or the 'identity' string. It returns the same object if it is
      a numpy array. It raises an exception otherwise.
  
      Parameters
      ----------
      obj : object
          any object
  
      Returns
      -------
      obj : object
          the same object given as argument if `obj` is None or a numpy
          array. None if `obj` is the 'identity' string.
      """
      if (obj is None) or isinstance(obj, np.ndarray):
          return obj
      if isinstance(obj, str) and (obj == "identity"):
          return None
      raise ValueError("Invalid matrix")
  
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 2 for calling the DiffeomorphicMap obj's underlying member method code with example usage: obj.interpret_matrix(obj) and returns: obj, None