docs: def add_params(self, p):
          """Add new variables or change values to be used for particular
          parameter names that will not be jointly varied."""
          new_params = p.copy()
          for key,val in new_params.items():
              if not isinstance(val, collections.Iterable):
                  new_params[key] = [new_params[key]]
              #_check_comb_param(key, val)
          self.comb_params.update(new_params)