def extend_range(min_max, extend_ratio=.2):
    """Symmetrically extend the range given by the `min_max` pair.
       The new range will be 1 + `extend_ratio` larger than the original range.
    """
    mme = (min_max[1] - min_max[0]) * extend_ratio / 2
    return (min_max[0] - mme, min_max[1] + mme)