def METHOD_NAME(self, p):
    # 源项
    x = p[...,0]
    y = p[...,1]
    pi = np.pi
    val = 2*pi**2*(3*np.cos(pi*x)**2*np.cos(pi*y)**2-np.cos(pi*x)**2-np.cos(pi*y)**2+1)*np.cos(pi*x)*np.cos(pi*y)
    return val