def six_hump_camel_func(x):
    """
    Definition of the six-hump camel
    """
    x1 = x[0]
    x2 = x[1]
    term1 = (4 - 2.1 * x1 ** 2 + x1 ** 4 / 3) * x1 ** 2
    term2 = x1 * x2
    term3 = (-4 + 4 * x2 ** 2) * x2 ** 2
    return term1 + term2 + term3
