'Two dimensional Mexican Hat model function'

@staticmethod
def evaluate(x, y, amplitude, x_0, y_0, sigma):

    rr_ww = ((((x - x_0) ** 2) + ((y - y_0) ** 2)) / (2 * (sigma ** 2)))
    return ((amplitude * (1 - rr_ww)) * np.exp((- rr_ww)))
