code: def free_parameter(self, name, par, free=True):
          
          name = self.get_source_name(name)
          if par in self._lck_params.get(name, []):
              return
          idx = self.like.par_index(name, par)
          self.like[idx].setFree(free)
          self._sync_params(name)
docs: Free/Fix a parameter of a source by name.
  
          Parameters
          ----------
          name : str
              Source name.
  
          par : str
              Parameter name.