On Mon, Mar 23, 2020 at 8:31 AM Elias Karabelas <karabelasel...@gmail.com> wrote:
> Dear Matt, > > I've just found this answer from 2014 > > https://lists.mcs.anl.gov/pipermail/petsc-users/2014-August/022450.html > > wondering if this would theoretically work. > > In serial certainly, I just don't see how it works in parallel since you might not own the row you need from the transpose. > And the thing with this FCT-Schemes is, that they're build on purely > algebraic considerations (like AMG) so I don't want to break it back down > to mesh information if possible at all. > The FEM-FCT I am familiar with from Lohner was phrased on a mesh. Thanks, Matt > Best regards > > Elias > On 23/03/2020 13:02, Matthew Knepley wrote: > > On Mon, Mar 23, 2020 at 7:46 AM Elias Karabelas <karabelasel...@gmail.com> > wrote: > >> Dear Users, >> >> I want to implement a FCT (flux corrected transport) scheme with PETSc. >> To this end I have amongst other things create a Matrix whose entries >> are given by >> >> L_ij = -max(0, A_ij, A_ji) for i neq j >> >> L_ii = Sum_{j=0,..n, j neq i} L_ij >> >> where Mat A is an (non-symmetric) Input Matrix created beforehand. >> >> I was wondering how to do this. My first search brought me to >> >> https://www.mcs.anl.gov/petsc/petsc-current/src/mat/examples/tutorials/ex16.c.html >> >> >> but this just goes over the rows of one matrix to set new values and now >> I would need to run over the rows and columns of the matrix. My Idea was >> to just create a transpose of A and do the same but then the row-layout >> will be different and I can't use the same for loop for A and AT and >> thus also won't be able to calculate the max's above. >> >> Any help would be appreciated >> > > I think it would likely be much easier to write your algorithm directly on > the mesh, rather than using matrices, since the locality information is > explicit with the mesh, but has to be reconstructed with the matrix. > > The problem here is that in parallel there would be no easy way to get the > halo you need using a matrix. You > really want the ghosted space for assembly, and that is provided by the DM > objects. Does this make sense? > Unless anybody in PETSc has a better idea. > > Thanks, > > Matt > > >> Best regards >> >> Elias >> >> > > -- > What most experimenters take for granted before they begin their > experiments is infinitely more interesting than any results to which their > experiments lead. > -- Norbert Wiener > > https://www.cse.buffalo.edu/~knepley/ > <http://www.cse.buffalo.edu/~knepley/> > > -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>