Tensor divergence seems to be wrong

[nicoguaro]

• Continuum Mechanics version: 0.2.2
• Python version: 3.7.10

Description

The divergence of the stress tensor is not 0 while the Navier-Cauchy operator is zero for the displacement vector.

What I Did

Paste the command(s) you ran and the output.
If there was a crash, please include the traceback here.

from sympy import *
from continuum_mechanics.vector import div_tensor
from continuum_mechanics.solids import navier_cauchy

r, theta, phi = symbols("r theta phi")
T, mu = symbols("T mu")

h = (1, r, r*sin(theta))
coords = (r, theta, phi)
disp = Matrix([[0], [0], [T*sin(theta)/(8*pi*mu*r**2)]])
stress = Matrix([[0, 0, -3*T*sin(theta)/(8*pi*r**3)], [0, 0, 0], [-3*T*sin(theta)/(8*pi*r**3), 0, 0]])

And

navier_cauchy(disp, [1, mu], coords, h)

gives Matrix([[0], [0], [0]]), while

div_tensor(stress, coords, h)

gives Matrix([[0], [0], [3*T*sin(theta)/(8*pi*r**4)]]).