How to rotate strain field?

Hi, developpers!!

I’m wondering how to rotate the strain field.
Is it possible?
I asked this question because I stumbled upon it.
I would appreciate it if you could tell me how to do this.

(I am not a developer, this is a community wiki)
I guess you have a solution u on a domain that is invariant under rotation (e.g. a disk) and you want to obtain R(u) with R some rotation.
I did that in the past by copying the mesh Th to a rotated version RTh (use function movemesh()), copy the dofs of the FE function u to the dofs (degrees of freedom) in the rotated mesh, in a new FE function v defined on RTh. Finally interpolate between the two meshes by setting w=v with w defined over Th. w approximates the rotated field Ru:

// not an actual code, just a suggestion
fespace Vh(Th, P2);
Vh u ,w;
// obtain u
// rotate the mesh Th to RTh
fespace RVh(RTh, P2);
RVh v;
for (int i=0; i<RVh.ndof; i++) v[][i]=u[][i];