docstr: calculate distance for current set of parameters.
          
docstr_tok: ["calculate","distance","for","current","set","of","parameters","."]
code: def distance(self, xopt):
      """calculate distance for current set of parameters."""
      pass
  
imports: import logging
  import abc
  from itertools import combinations
  import numpy
  from dipy.core.optimize import Optimizer
  from dipy.align.bundlemin import _bundle_minimum_distance, _bundle_minimum_distance_asymmetric, distance_matrix_mdf
  from dipy.tracking.streamline import transform_streamlines, unlist_streamlines, center_streamlines, set_number_of_points, select_random_set_of_streamlines, length, Streamlines
  from dipy.segment.clustering import qbx_and_merge
  from dipy.core.geometry import compose_transformations, compose_matrix, decompose_matrix
  from time import time
label_desc: Use image node_id 3 for calling the StreamlineDistanceMetric obj's underlying member method code with example usage: obj.distance(xopt) without return types