class_docstr: A class that encodes trial index information.  It has a list of
  model names and a list of test segment names and a matrix
  indicating which combinations of model and test segment are
  trials of interest.
  
  Arguments
  ---------
  modelset : list
      List of unique models in a ndarray.
  segset : list
      List of unique test segments in a ndarray.
  trialmask : 2D ndarray of bool.
      Rows correspond to the models and columns to the test segments. True, if the trial is of interest.
docstr: Saves the object in pickle format
docstr_tok: ["Saves","the","object","in","pickle","format"]
code: def save_ndx_object(self, output_file_name):
      """Saves the object in pickle format"""
      with open(output_file_name, "wb") as output:
          pickle.dump(self, output, pickle.HIGHEST_PROTOCOL)
  
imports: import numpy
  import copy
  import pickle
  from scipy import linalg
label_desc: Use image node_id 2 for calling the Ndx obj's underlying member method code with example usage: obj.save_ndx_object(output_file_name) without return types