docstr: Compute streamlines barycenter
docstr_tok: ["Compute","streamlines","barycenter"]
code: def _slines_barycenters(self, slines_arr):
      """Compute streamlines barycenter"""
      return np.mean(slines_arr, axis=1)
  
file_path: dipy/dipy/segment/fss.py
imports: import warnings
  import numpy
  from scipy.sparse import coo_matrix
  from scipy.spatial import cKDTree
  from dipy.tracking.streamline import set_number_of_points
  from dipy.segment.metric import mean_euclidean_distance
  from dipy.io.stateful_tractogram import StatefulTractogram
label_desc: Use image node_id 4 for calling the FastStreamlineSearch obj's underlying member method code with example usage: obj._slines_barycenters(slines_arr) and returns: np