code: def _pre_compute_secondary(self, positive_vals, negative_vals):
          
          self._secondary_min = (
              negative_vals and min(min(negative_vals), self.zero)
          ) or self.zero
          self._secondary_max = (
              positive_vals and max(max(positive_vals), self.zero)
          ) or self.zero
docs: Compute secondary y min and max