code: def constrain_fixed(self, value=None, warning=True, trigger_parent=True):
          
          if value is not None:
              self[:] = value
  
          #index = self.unconstrain()
          index = self._add_to_index_operations(self.constraints, np.empty(0), __fixed__, warning)
          self._highest_parent_._set_fixed(self, index)
          self.notify_observers(self, None if trigger_parent else -np.inf)
          return index
docs: Constrain this parameter to be fixed to the current value it carries.
  
          This does not override the previous constraints, so unfixing will
          restore the constraint set before fixing.
  
          :param warning: print a warning for overwriting constraints.