def bench5(x):
    """A benchmark function for test purposes.

        f(x) = float(x[0]) ** 2 + x[1] ** 2

    where x is a string. It has a single minima with f(x) = 0 at x[0] = "0"
    and x[1] = "0"
    This benchmark is used for checking support of mixed spaces.
    """
    return float(x[0]) ** 2 + x[1] ** 2
