1 static char help[] = "Introductory example that illustrates running PETSc on a subset of processes.\n\n"; 2 3 #include <petscsys.h> 4 5 int main(int argc, char *argv[]) 6 { 7 PetscMPIInt rank, size; 8 9 /* We must call MPI_Init() first, making us, not PETSc, responsible for MPI */ 10 PetscCallMPI(MPI_Init(&argc, &argv)); 11 #if defined(PETSC_HAVE_ELEMENTAL) 12 PetscCall(PetscElementalInitializePackage()); 13 #endif 14 /* We can now change the communicator universe for PETSc */ 15 PetscCallMPI(MPI_Comm_rank(MPI_COMM_WORLD, &rank)); 16 PetscCallMPI(MPI_Comm_split(MPI_COMM_WORLD, rank%2, 0, &PETSC_COMM_WORLD)); 17 18 /* 19 Every PETSc routine should begin with the PetscInitialize() routine. 20 argc, argv - These command line arguments are taken to extract the options 21 supplied to PETSc and options supplied to MPI. 22 help - When PETSc executable is invoked with the option -help, 23 it prints the various options that can be applied at 24 runtime. The user can use the "help" variable place 25 additional help messages in this printout. 26 */ 27 PetscCall(PetscInitialize(&argc, &argv, (char*) 0, help)); 28 29 /* 30 The following MPI calls return the number of processes 31 being used and the rank of this process in the group. 32 */ 33 PetscCallMPI(MPI_Comm_size(PETSC_COMM_WORLD,&size)); 34 PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD,&rank)); 35 36 /* 37 Here we would like to print only one message that represents 38 all the processes in the group. We use PetscPrintf() with the 39 communicator PETSC_COMM_WORLD. Thus, only one message is 40 printed representng PETSC_COMM_WORLD, i.e., all the processors. 41 */ 42 PetscCall(PetscPrintf(PETSC_COMM_WORLD,"Number of processors = %d, rank = %d\n", size, rank)); 43 44 /* 45 Always call PetscFinalize() before exiting a program. This routine 46 - finalizes the PETSc libraries as well as MPI 47 - provides summary and diagnostic information if certain runtime 48 options are chosen (e.g., -log_view). See PetscFinalize() 49 manpage for more information. 50 */ 51 PetscCall(PetscFinalize()); 52 PetscCallMPI(MPI_Comm_free(&PETSC_COMM_WORLD)); 53 #if defined(PETSC_HAVE_ELEMENTAL) 54 PetscCall(PetscElementalFinalizePackage()); 55 #endif 56 /* Since we initialized MPI, we must call MPI_Finalize() */ 57 PetscCallMPI(MPI_Finalize()); 58 return 0; 59 } 60 61 /*TEST 62 63 test: 64 nsize: 5 65 args: -options_left no 66 filter: sort -b | grep -v saws_port_auto_selectcd 67 filter_output: sort -b 68 69 TEST*/ 70