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 PetscMPIInt rank, size; 7 8 /* We must call MPI_Init() first, making us, not PETSc, responsible for MPI */ 9 PetscCallMPI(MPI_Init(&argc, &argv)); 10 #if defined(PETSC_HAVE_ELEMENTAL) 11 PetscCall(PetscElementalInitializePackage()); 12 #endif 13 /* We can now change the communicator universe for PETSc */ 14 PetscCallMPI(MPI_Comm_rank(MPI_COMM_WORLD, &rank)); 15 PetscCallMPI(MPI_Comm_split(MPI_COMM_WORLD, rank % 2, 0, &PETSC_COMM_WORLD)); 16 17 /* 18 Every PETSc routine should begin with the PetscInitialize() routine. 19 argc, argv - These command line arguments are taken to extract the options 20 supplied to PETSc and options supplied to MPI. 21 help - When PETSc executable is invoked with the option -help, 22 it prints the various options that can be applied at 23 runtime. The user can use the "help" variable place 24 additional help messages in this printout. 25 */ 26 PetscFunctionBeginUser; 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