Matthew Knepley via petsc-users <petsc-users@mcs.anl.gov> writes: > On Fri, Sep 20, 2019 at 7:54 AM Bao Kai via petsc-users < > petsc-users@mcs.anl.gov> wrote: > >> Hi, >> >> I understand that PETSc is not designed to be used this way, while I >> am wondering if someone have done something similar to this. >> >> We have the full matrix from a simulation and rhs vector. We would >> like to read in through PETSc in one process, then we use some >> partition functions to partition the matrix. >> >> Based on the partition information, we redistribute the matrix among >> the processes. Then we solve it in parallel. It is for testing the >> performance of some parallel linear solver and preconditions. >> >> We are not in the position to develop a full parallel implementation >> of the simulator yet.
An alternative is to assemble a Mat living on a parallel communicator, but with all entries on rank 0 (so just call your serial code to build the matrix). You can do the same for your vector, then KSPSolve. To make the solver parallel, just use run-time options: -ksp_type preonly -pc_type redistribute will redistribute automatically inside the solver and return the solution vector to you on rank 0. You can control the inner solver via prefix -redistribute_ksp_type gmres -redistribute_pc_type gamg -redistibute_ksp_monitor
