Hi, I am trying to extract vorticity from the velocity field for fluid simulation. This is my code and extracted field. I am wondering why the vorticity field is so large that it ranges from -160 to 160. Am I doing the computation wrongly?

```
// We have a known mesh in the file fname
mesh = gen_mesh_from_file(fnames)
nodes = mesh.coordinates()
cell = mesh.cells()
// define function space
V = VectorFunctionSpace(mesh, "Lagrange", 2)
Q = FunctionSpace(mesh, "Lagrange", 1)
u_n = Function(V)
// We have a vector field u_n in second order VectorFunctionSpace, and we compute vorticity from that
ux, uy = u_n.split(deepcopy=True)
vortex = ux.dx(1)-uy.dx(0)
vor = Function(Q)
vor = project(vortex,Q)
// We plot the vorticity
np_solution = vor.compute_vertex_values()
plot_fig = plt.tricontourf(nodes[:,0], nodes[:,1],cell,np_solution,levels=100,cmap=cmocean.cm.thermal)
```

velocity field:

vorticity: