code: def _compute_variables_indices(self):
          
  
          counter_objective = 0
          counter_model     = 0
  
          for variable in self.space_expanded:
              variable.set_index_in_objective([counter_objective])
              counter_objective +=1
  
              if variable.type is not 'categorical':
                  variable.set_index_in_model([counter_model])
                  counter_model +=1
              else:
                  num_categories = len(variable.domain)
                  variable.set_index_in_model(list(range(counter_model,counter_model + num_categories)))
                  counter_model +=num_categories
docs: Computes and saves the index location of each variable (as a list) in the objectives
          space and in the model space. If no categorical variables are available, these two are
          equivalent.