Thanks Matthew, i have made some progress but i am still unsure on how to proceed to make the DMDAs work as intended, i will try to lay out what i am trying now:
I was able to port the interpolation into the DMDA model but it works only in serial runs, and it becomes unstable for more than one processor running, What i do is roughly this: - Calculate density at a cell-centered DMDA object, using a local vector so i can access the ghost rows (indices -1 and max+1) - Interpolate into a face-centered DMDA object for velocities, using also a local vector. Doing this i get the right results using the same interpolation i used for my non-petsc implementation of the model, as long as i use only one processor but the doubts i have are: - How to use the local vectors properly: Is operating on them the recommended course in this case? - How can i access the ghost indices in the global vector so i can then communicate GlobalToLocal? would this be a better strategy? - I feel is wrong to interpolate a cell-centered based vector into a face-centered based vector, using the indices of the latter, what strategy would work best in this case? I also tried opening a global vector with a different DA layout than the one created (opening global density on the velocities DMDA layout) and this introduced an error in the GlobalToLocal, LocalToLocal, LocalToGlobal communication, something didn't happen if i used the local versions of these vectors instead, Thanks for your help, Manuel On Sat, Oct 6, 2018 at 4:45 AM Matthew Knepley <knep...@gmail.com> wrote: > On Fri, Oct 5, 2018 at 6:49 PM Manuel Valera <mvaler...@sdsu.edu> wrote: > >> Hello, >> >> I'm trying to do a simple variable interpolation, from a cell center to a >> face in a staggered grid, my model data management is done with DMDAs, with >> two different DMs one for each cell position, >> >> I already did this task on a fortran only version of the model using the >> 4 closest neighbors of the scalars (cell center) to be interpolated at the >> velocity site (cell face), i did it using a loop over the domain, somehow >> this easy task is not translating into the DMDA framework, >> > > Its not clear to me what problem you are having. We have done this before. > For example, > > > https://www.mcs.anl.gov/petsc/petsc-current/src/snes/examples/tutorials/ex30.c.html > > I would note that the development version of PETSc now has DMStag which > supports staggered grid discretizations directly. > > Thanks, > > Matt > > >> I'm not sure what I'm doing wrong or not aware of a easier way Petsc may >> have for this task, if you could point out an easier strategy or an example >> I would be grateful, >> >> Thanks, >> >> >> >> >> > > -- > 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/> >