def _compute_box(self, positive_vals, negative_vals):
        """Compute Y min and max"""
        max_ = max(
            max(positive_vals or [self.zero]),
            max(negative_vals or [self.zero])
        )

        if self.range and self.range[0] is not None:
            self._box.ymin = self.range[0]
        else:
            self._box.ymin = -max_

        if self.range and self.range[1] is not None:
            self._box.ymax = self.range[1]
        else:
            self._box.ymax = max_
Compute Y min and max