Re: Questions on parallel::distributed::GridRefinement::refine_and_coarsen_fixed_number in deal.II 9.0.1 released

[Wolfgang Bangerth]

> Dear Wolfgang Bangerth,
>
>   Recently, I use your deal.II (Version 9.0.1)

It's really not *my* program any more -- more than 250 people have contributed
to it by now :-)


> to solve a group of PDEs
> (haveing a wave-like solution whose amplitude is modulated by another smoother
> field). However, I encounter a problem: Function
> parallel::distributed::GridRefinement::refine_and_coarsen_fixed_number
> (tria, criteria, top_fraction_of_cells, bottom_fraction_of_cells,  max_n_cells
> ) cannot always refine my grid (in my case, it is actually coarsening my grid)
> even if  bottom_fraction_of_cells = 0 and max_n_cells =
> pow(2,dim)*Triangulation::n_active_cells() .

What are the criteria you have? Does the vector have only zeros in it? What is
top_fraction?


>  I check the manual of deal.II
> and find that refine levels of adjecent cells cannot exceed one which maybe
> the reason for my problem.

No, that should really not be the issue.

Best
W.

--
------------------------------------------------------------------------
Wolfgang Bangerth email: bang...@colostate.edu
www: http://www.math.colostate.edu/~bangerth/

[Wolfgang Bangerth]

On 10/12/19 6:50 AM, 王昆 wrote:
>
> At the first time step, the criteria only have two values, i.e., 0.0 and
> 0.163. And only 6% cells have the larger value. No matter I set the
> top_fraction to a value below or above 0.163 (bottom_fraction_of_cells remains
> zero), I can not obtain a finer grid (the result cell number is smaller the
> orignial one). Although the cells with the larger criteria are finer than the
> ones with smaller criteria, it is actually a result that grid coarsening
> happens at cells with smaller criteria while the cells with larger criteria do
> not change.
> How can I refine my grid in this case?

It's difficult for me to debug your problem from a distance. But I'd like to
point out that the function you call,
parallel::distributed::GridRefinement::refine_and_coarsen_fixed_number, takes
as argument a *fraction of the cells*, not a value for the error indicator
above which the cells should be refined. What happens if you set the top
fraction to 1.0 and the bottom fraction 0.0?

Best
WB