我正在玩广义相对论，我几乎完成了。但是当我使用 sympy.dsolve 求解测地线方程时，我总是报告“NotImplementedError”。我的代码如下所示：
from gravipy.tensorial import *
from sympy import *
t, r, theta, phi = symbols('t, r, theta, phi')
tau = Symbol('tau')
coord = [s(tau) for s in symbols('t, r, theta, phi', cls=Function)]
chi = Coordinates('chi', [t, r, theta, phi])
M = Symbol('M')
Metric = diag(-(1 - 2 * M / r), 1 / (1 - 2 * M / r), r ** 2,
r ** 2 * sin(theta) ** 2)
g = MetricTensor('g', chi, Metric)
pprint(g(All, All))
christoffel = Christoffel('gamma', g)
geodesics = Geodesic('geodesics', g, tau)
set_ = []
for i, j in zip(tuple(geodesics(All)), coord):
pprint(solve(i, Derivative(j, (tau, 2)), dict=True)[0])
set_.append(Eq(Derivative(j, (tau, 2)), solve(i, Derivative(j, (tau, 2)), dict=True)[0][Derivative(j, (tau, 2))]))
pprint(dsolve(set_))
有谁知道如何解决这个问题？