1! 2! This introductory example illustrates running PETSc on a subset 3! of processes 4! 5! ----------------------------------------------------------------------- 6 7program main 8#include <petsc/finclude/petscsys.h> 9 use petscmpi ! or mpi or mpi_f08 10 use petscsys 11 implicit none 12 13 PetscErrorCode ierr 14 PetscMPIInt rank, size, zero, two 15 16! We must call MPI_Init() first, making us, not PETSc, responsible 17! for MPI 18 19 PetscCallMPIA(MPI_Init(ierr)) 20 21! We can now change the communicator universe for PETSc 22 23 zero = 0 24 two = 2 25 PetscCallMPIA(MPI_Comm_rank(MPI_COMM_WORLD, rank, ierr)) 26 PetscCallMPIA(MPI_Comm_split(MPI_COMM_WORLD, mod(rank, two), zero, PETSC_COMM_WORLD, ierr)) 27 28! Every PETSc routine should begin with the PetscInitialize() 29! routine. 30 31 PetscCallA(PetscInitialize(ierr)) 32 33! The following MPI calls return the number of processes being used 34! and the rank of this process in the group. 35 36 PetscCallMPIA(MPI_Comm_size(PETSC_COMM_WORLD, size, ierr)) 37 PetscCallMPIA(MPI_Comm_rank(PETSC_COMM_WORLD, rank, ierr)) 38 39! Here we would like to print only one message that represents all 40! the processes in the group. 41 if (rank == 0) write (6, 100) size, rank 42100 format('No of Procs = ', i4, ' rank = ', i4) 43 44! Always call PetscFinalize() before exiting a program. This 45! routine - finalizes the PETSc libraries as well as MPI - provides 46! summary and diagnostic information if certain runtime options are 47! chosen (e.g., -log_view). See PetscFinalize() manpage for more 48! information. 49 50 PetscCallA(PetscFinalize(ierr)) 51 PetscCallMPIA(MPI_Comm_free(PETSC_COMM_WORLD, ierr)) 52 53! Since we initialized MPI, we must call MPI_Finalize() 54 55 PetscCallMPIA(MPI_Finalize(ierr)) 56end 57 58! 59!/*TEST 60! 61! test: 62! 63!TEST*/ 64