By the way, this function has just been introduced in April with #12003 <https://github.com/dealii/dealii/pull/12003>. Suggestions for improvement on this new feature are welcome!
Best, Marc On Friday, June 25, 2021 at 12:37:31 PM UTC-6 Marc Fehling wrote: > Hi Alex, > > > I scrolled through grid_generator.cc and found that subdivided_cylinder > has a hardcoded epsilon of 1e-5 for determining whether a face is at the > boundary. Of course, with a system of my size, all faces will end up being > considered to be at the boundary. > > > > Because it not only sets the boundary ids, but the manifold ids, it > seems I will have to modify the subdivided_cylinder to make the epsilon > value much smaller or somehow relative to the system size, which is simple > enough. > > That sounds like a good idea to me. Would you willing to write a patch and > open a pull request for the library? I'm sure others will benefit of your > changes as well! > > There are several options you can consider. > > 1. You could provide epsilon as a parameter to the function and > default it to `1e-5`. > 2. Instead of an absolute threshold, you can introduce a relative one, > for example, `epsilon * cell->diameter()` or something similar. > 3. You can also try to use the machine precision > std::numeric_limits<T>::epsilon > <https://en.cppreference.com/w/cpp/types/numeric_limits/epsilon> as a > substitute for `1e-5`. > 4. Why do we need these epsilons in the first place? Maybe it will > work if you just replace the greater/lesser checks with their equal > variants `>=` and `<=`. > > Best, > Marc > > On Friday, June 25, 2021 at 6:45:12 AM UTC-6 alexanderc...@gmail.com > wrote: > >> I have been trying to construct a system that is small (a total length of >> 1e-5 m) with the subdivided cylinder grid generator. However, I have been >> having trouble with the boundary indicators. I wanted to set my own >> boundaries, and because there is no colorize option (it defaults to setting >> the left end face of the cylinder to 1, and the right end to 2), I tried to >> first set all boundary ids to 0. However, this leads to the following >> exception: >> >> terminate called after throwing an instance of >> 'dealii::TriaAccessorExceptions::ExcNoPeriodicNeighbor' >> what(): >> -------------------------------------------------------- >> An error occurred in line <2597> of file >> </home/ipausers/cumberworth/src/dealii-9.3.0/source/grid/tria_accessor.cc> >> in function >> dealii::TriaIterator<dealii::CellAccessor<dim, spacedim> > >> dealii::CellAccessor<dim, spacedim>::neighbor_or_periodic_neighbor(unsigned >> int) const [with int dim = 3; int spacedim = 3] >> The violated condition was: >> false >> Additional information: >> (none) >> >> Since in my test system, I was setting the boundary ids to be the same as >> the default, I tried to rely on this instead. However, I was having strange >> behaviour where it seemed that the entire system was having the boundary >> conditions applied to it. I scrolled through grid_generator.cc and found >> that subdivided_cylinder has a hardcoded epsilon of 1e-5 for determining >> whether a face is at the boundary. Of course, with a system of my size, all >> faces will end up being considered to be at the boundary. >> >> Because it not only sets the boundary ids, but the manifold ids, it seems >> I will have to modify the subdivided_cylinder to make the epsilon value >> much smaller or somehow relative to the system size, which is simple enough. >> >> It would probably also be good to have the colorize option. However, I am >> not sure what to make of the exception when I try to set all the boundary >> ids to 0. >> >> Best, >> Alex >> > -- The deal.II project is located at http://www.dealii.org/ For mailing list/forum options, see https://groups.google.com/d/forum/dealii?hl=en --- You received this message because you are subscribed to the Google Groups "deal.II User Group" group. To unsubscribe from this group and stop receiving emails from it, send an email to dealii+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/dealii/70c57a19-cd2e-4950-afd8-e8890aab1491n%40googlegroups.com.
