This sort of feedback is great in terms of learning what can move out of "tutorials" and into "tests". https://gitlab.com/petsc/petsc/-/merge_requests/2629
Am Di., 24. März 2020 um 16:22 Uhr schrieb Jed Brown <[email protected]>: > Mark Adams <[email protected]> writes: > > > Good question. It does look like there is Q1: > > > > src/dm/impls/da/da.c:- ctype - DMDA_Q1 and DMDA_Q0 are currently the > only > > supported forms > > > > And in looking at a cell centered > > example src/snes/examples/tutorials/ex20.c, it looks like only DMDA_Q1 > > works. I get an error when I set it to DMDA_Q0 (DMDA_Q1 is the default). > > This is puzzling, Q0 is natural in cell centered. > > The comments in those examples are kinda wrong -- they never told the DM > it was cell-centered so it uses a multigrid that isn't compatible with > the boundary conditions. The interpolation is Q1 on the dual grid, not > conservative Q1 on cells. > > > I am not familiar with DMDA and I don't understand why, from ex20, that > you > > have an odd number of points on a cell centered grid and an even number > for > > vertex centered (eg, ex14). I would think that it should be the opposite. > > The example is bad. >
