How to reset a metric to cleared state?

Developers Help
#1

Dear forum, in general, the function

MMG2D_mmg2dlib(mesh, met)

is not idempotent: calling it repeatedly gives different results than calling it once. Regardless of whether it makes sens to call it repeatedly, I wondered how not to make use of the metric computed in the first call.
If met->np was zero before the first call, it is !=0 after the first call. So, I wondered how to reset it to a state with met->np == 0. Just setting met->np = 0 works but it is not an API function (and maybe it leads to a memory leak somewhere). On the other hand, freeing the solution with the API function

MMG2D_Free_solutions(mesh, met)

between the calls does not work: it gives the message ##ERROR: WRONG DATA TYPE in the second call.
I feel there should be an API function to clear a solution/metric since I don’t want to touch the internals of mmg because they can change in the future. What API function should I use to reset a metric/solution to the state it was left after a call to

MMG2D_Init_mesh(MMG5_ARG_start, MMG5_ARG_ppMesh, &mesh, MMG5_ARG_ppMet, &met, MG5_ARG_end

?
Thank you.

#2

Hi Mathias,

Most of time, people uses iterative call of MMG2D_mmg2dlib in the context of the mesh adaptation to a solution. In this case they provide a metric computed from the solution between each call of mmg so it works without any issue.

In your case, I totally agree that touching the internal structure of Mmg is not a good idea and that I should provide APIs to reset it. I have tried to patch the error in a such way that after the call to MMG2D_Free_solutions :

  • you can call MMG2D_mmg2dlib without error (the structure is in a state compatible with the state it had after the MMG2D_Init_mesh call);
  • you can use MMG2D_Set_solSize and MMG2D_Set_.*Sol to set a new metric;
  • I hope that the function is still compatible with your PR #70.

For now you can test the correction in the branch feature/cleaned-free-solutions-API. I let you confirm if it works on your test case and I will merge it into the develop branch.

By the way, I will also add the equivalent MMG*_Free_solutions functions in mmgs and mmg3d.

Regards,

Algiane

#3

Thank you for the answer. Yes, that looks as if it’ll do the trick!

#4

Hello Mathias,

Thank you for your feedback. It is merged in the develop now.

Have a nice day

#5

Ok, thank you!
Mathias