code: def free_parameters(self):
          
  
          # Refresh the list
  
          self._update_parameters()
  
          # Filter selecting only free parameters
  
          free_parameters_dictionary = collections.OrderedDict()
  
          for parameter_name, parameter in self._parameters.iteritems():
  
              if parameter.free:
  
                  free_parameters_dictionary[parameter_name] = parameter
  
          return free_parameters_dictionary
docs: Get a dictionary with all the free parameters in this model
  
          :return: dictionary of free parameters