Cannot determine geometric dimension from expression

[dokken]

@ss780060872

tion(V)
solve(lhs(F) == rhs(F), u)

for n in range(num_steps):

solve(lhs(F) == rhs(F), u)
u_n.assign(u)  
plot(u)

Please format your code as

```python
# add code here
```

Also, please search the forum for your error message, as there are many similar posts, including: Error while trying to find the derivative of user-defined expression ["ufl.log.UFLException: Cannot determine geometric dimension from expression."] - #2 by kamensky
which I believe has the solution to your problem.