def sphere_pos(self, x):
        """Sphere (squared norm) test objective function"""
        # return np.random.rand(1)[0]**0 * sum(x**2) + 1 * np.random.rand(1)[0]
        c = 0.0
        if x[0] < c:
            return np.nan
        return -c**2 + sum((x + 0)**2)