python - 收到错误 : can't convert expression to float

Question

我是 python 的新手，我正在尝试查找 Christoffel symbols表面上的黎曼度量，但出现此错误:TypeError: can't convert expression to float。为简单起见，我编写了另一个错误完全相同的代码(我的基本代码很长且不可读，所以我尝试了这个示例代码来理解我的错误)。这是我的示例代码:

from sympy import *
import numpy as np

coor = symbols('x y')

x = [coor[0] ** 2, coor[1]]


christoffels = np.zeros((2,2))

for i in range(2):
    for j in range(2):
        christoffels[i][j] = x[i] * x[j]


print(christoffels)

你能告诉我哪里出了问题吗？

Answer 1

作业存在多个问题:

christoffels[i][j] = x[i] * x[j]

右边是symbols，左边是NumPy floats array cell。

因此 Python 很难将 symbols 转换为 float 。

TypeError: can't convert expression to float

让我们通过将矩阵定义为 sympy matrix 来修复它:

from sympy import *
import numpy as np

coor = symbols('x y')

x = [coor[0] ** 2, coor[1]]


# Create sympy array
christoffels = zeros(2,2)

for i in range(2):
    for j in range(2):
        # Now assignment works
        # NOTE: In sympy location denoted as [i, j] and not [i][j]
        christoffels[i, j] = x[i] * x[j]

# Matrix([[x**4, x**2*y], [x**2*y, y**2]])
print(christoffels)