test_euler.py 文件源码

def test_euler_sineg():
    psi = Function('psi')
    t = Symbol('t')
    x = Symbol('x')
    L = D(psi(t, x), t)**2/2 - D(psi(t, x), x)**2/2 + cos(psi(t, x))
    assert euler(L, psi(t, x), [t, x]) == [Eq(-sin(psi(t, x)) -
                                              D(psi(t, x), t, t) +
                                              D(psi(t, x), x, x))]