[petsc-users] PETSc within a larger simulation

[Barry Smith]

> On Mar 20, 2015, at 1:02 PM, Young, Matthew, Adam <may at bu.edu> wrote:
> 
> I have a PETSc routine that I am trying to use as an electric-field solver within a particle-in-cell code. The existing PIC code is parallelized with MPI. The pure PIC code (written many years ago by my advisor) is well-tested and I am trying to add an option for it to operate as a hybrid fluid/PIC code. This requires solving Ax=b at every time step but I don't think I understand how to manage communication between the existing code and my PETSc solver. Since we may not always run the hybrid version, the code calls MPI_Init() before PetscInitialize(). Section 14.1 of the manual suggests that I use PetscSetCommWorld between MPI_Init() and PetscInitialize(), but that routine appears to not be supported anymore. Is that correct? Can you point me to examples of simulations that use PETSc within a larger code?

   Matt,

    In the standard case where the PIC and fluid code are both running on the same communicator (MPI_COMM_WORLD) you don't need to do anything special, just call the MPI_Init() and then the PetscInitialize(). If the PETSc code runs on a smaller communicator then BEFORE the call to PetscInitialize() you just need to set PETSC_COMM_WORLD = comm (where comm is that smaller communicator). (This replaces the use of the function call PetscSetCommWorld() that once existed.)

  Barry

> 
> --Matt
> 
> --------------------------------------------------------------
> Matthew Young
> Graduate Student
> Boston University Dept. of Astronomy
> --------------------------------------------------------------