Skip adaption if error is small

[bonh]

As one can see from the following output, the meshes before and after the adaption step are virtually the same. Nevertheless, I assume, that the mesh is updated inside Omega_h. Now, if the mesh changes, I have to reconstruct my preconditioner - even, if the mesh does not really change. And this steps takes a lot of time...

Now my question: Is it possible to introduce some kind of feedback from Omega_h's adapt if the mesh has changed "a lot", e.g., a boolean. Then I could use this boolean to skip the recreation of my preconditioner. @ibaned or do you have a different solution?

limited gradation in 1 steps
generated metrics in 0.0552537 seconds
before adapting:
21326 tets, quality [0.30,1.00], 21326 >0.30
26608 edges, length [0.25,1.55], 2536 <0.71, 24052 in [0.71,1.41], 20 >1.41
after adapting:
21334 tets, quality [0.30,1.00], 21334 >0.30
26624 edges, length [0.25,1.55], 2541 <0.71, 24076 in [0.71,1.41], 7 >1.41
addressing edge lengths took 0.179833 seconds
addressing element qualities took 0.0247778 seconds
adapting took 0.205315 seconds

[ibaned]

This is a reasonable idea at a high level... I just don't know how to define "a lot" in preconditioner terms, and even one small adaptation can remove or add a row to the matrix, so I'm not sure what the best procedure is for updating a preconditioner just enough to be compatible with the new mesh...

[bonh]

Well, let me clarify my question: In my simulation code I am doing something like that:

old_mesh # generate initial mesh
new_mesh = old_mesh
old_result # generate initial data
new_result = old_result
while t<t_end: # time loop
    t+=1
    model.init(new_mesh) # initialize data and solvers, preconditioners, ...
    old_result.interpolate(new_result)
    new_result = model.solve(old_result) # my pde code
    new_mesh = adapt_mesh(old_mesh, new_result) # omega_h    

Now, what I want to do is:

old_mesh # generate initial mesh
new_mesh = old_mesh
old_result # generate initial data
new_result = old_result
while t<t_end: # time loop
    t+=1
    if mesh_change_in_percent > 0.01:
        model.init(new_mesh) # initialize data and solvers, preconditioners, ...
    old_result.interpolate(new_result)
    new_result = model.solve(old_result) # my pde code
    new_mesh, mesh_change_in_percent = adapt_mesh(old_mesh, new_result) # omega_h    

So, if omega_h returns some kind of value ('mesh_change_in_percent`), which represents the amount of mesh changes, I can use this value in my higher level code to decide if I want to use the new mesh (leading to a re-initialization of all solver structures) or reuse the old mesh (with reusing the old solver structures). I am not sure which return value makes sense though...

[ibaned]

An alternative approach that I use in other code to avoid adapting too often is to have "trigger" quality and length definitions:

    AdaptOpts opts(&mesh);
    auto trigger_quality = opts.min_quality_desired - 0.02;
    auto trigger_length_ratio = opts.max_length_allowed * 0.9);

Then only adapt if the quality or length goes below the trigger:

while (t < t_end) {
  t += 1;
  // interpolate, solve etc...
  set_metric_based_on_result(mesh, new_result);
  auto minqual = mesh.min_quality();
  auto maxlen = mesh.max_length();
  if (minqual < trigger_quality || maxlen > trigger_length_ratio) {
     // adapt, re-init, etc...
  }
}

[bonh]

Mhh, that sounds interesting!

What is set_metric_based_on_result(mesh, new_result);?

[ibaned]

@bonh that is a placeholder for your own code that computes a metric field based on the current simulation state