Extract Iso Surface in 3D


Hi everyone,
I recently installed FreeFem because I am interested in the 3d mesh adaption routines (very satisified with that so far).

My problem right now is, that I want to solve a 3 dimensional PDE (with a scalar solution “u”) but I want to have boundary condition on the 2d surface where u=u_fix (just for the next time step).

Is there a smart (efficient) way to extract the iso mesh computational efficient and include a “int2d” boundary condition (du/dn=f(x,y,z))

(I have some Fortran code of my “old” naive solution without adaptive mesh algorithms, but I am not “willing” to port my bad code to FF++).
I know the 2d isoline function (but to my knowledge nothing like this exists for 3d).

Every bit of help is appreciated!



The solution “I came up with” utilizes “trunc” - but I only obtain a 3d mesh from that if i use “>” operator.
For “==” i get no results (because its unlikely to exaclity hit u==ufix on the any node).


Hi, i am still looking for a solution of the previous problem.

Furthermore, I want to solve a 2d equation on one surface of a 3d mesh, then transform the 3d mesh accordingly to the 2d solution.
Is there any smart way to do that? (I want to utilize movemesh, but right now i am not able to adress the 2d submesh)

Thank you