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 PetscFunctionBeginUser; 28 PetscCall(PetscInitialize(&argc, &argv, (char *)0, help)); 29 30 /* 31 The following MPI calls return the number of processes 32 being used and the rank of this process in the group. 33 */ 34 PetscCallMPI(MPI_Comm_size(PETSC_COMM_WORLD, &size)); 35 PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD, &rank)); 36 37 /* 38 Here we would like to print only one message that represents 39 all the processes in the group. We use PetscPrintf() with the 40 communicator PETSC_COMM_WORLD. Thus, only one message is 41 printed representng PETSC_COMM_WORLD, i.e., all the processors. 42 */ 43 PetscCall(PetscPrintf(PETSC_COMM_WORLD, "Number of processors = %d, rank = %d\n", size, rank)); 44 45 /* 46 Always call PetscFinalize() before exiting a program. This routine 47 - finalizes the PETSc libraries as well as MPI 48 - provides summary and diagnostic information if certain runtime 49 options are chosen (e.g., -log_view). See PetscFinalize() 50 manpage for more information. 51 */ 52 PetscCall(PetscFinalize()); 53 PetscCallMPI(MPI_Comm_free(&PETSC_COMM_WORLD)); 54 #if defined(PETSC_HAVE_ELEMENTAL) 55 PetscCall(PetscElementalFinalizePackage()); 56 #endif 57 /* Since we initialized MPI, we must call MPI_Finalize() */ 58 PetscCallMPI(MPI_Finalize()); 59 return 0; 60 } 61 62 /*TEST 63 64 test: 65 nsize: 5 66 args: -options_left no 67 filter: sort -b | grep -v saws_port_auto_selectcd 68 filter_output: sort -b 69 70 TEST*/ 71