1 static char help[] = "Introductory example that illustrates running PETSc on a subset of processes.\n\n"; 2 3 /*T 4 Concepts: introduction to PETSc; 5 Concepts: process^subset set PETSC_COMM_WORLD 6 Processors: 2 7 8 Note that this example is not checking the error codes from the MPI calls with CHKERRQ() before PETSc is initialized 9 and after PETSc is finalized. This is because the PETSc macro CHKERRQ() will not work in those circumstances. 10 T*/ 11 #include <petscsys.h> 12 13 int main(int argc, char *argv[]) 14 { 15 PetscErrorCode ierr; 16 PetscMPIInt rank, size; 17 18 /* We must call MPI_Init() first, making us, not PETSc, responsible for MPI */ 19 ierr = MPI_Init(&argc, &argv);if (ierr) return ierr; 20 21 /* We can now change the communicator universe for PETSc */ 22 ierr = MPI_Comm_rank(MPI_COMM_WORLD, &rank);if (ierr) return ierr; 23 ierr = MPI_Comm_split(MPI_COMM_WORLD, rank%2, 0, &PETSC_COMM_WORLD);if (ierr) return ierr; 24 25 /* 26 Every PETSc routine should begin with the PetscInitialize() routine. 27 argc, argv - These command line arguments are taken to extract the options 28 supplied to PETSc and options supplied to MPI. 29 help - When PETSc executable is invoked with the option -help, 30 it prints the various options that can be applied at 31 runtime. The user can use the "help" variable place 32 additional help messages in this printout. 33 */ 34 ierr = PetscInitialize(&argc, &argv, (char*) 0, help);if (ierr) return ierr; 35 36 /* 37 The following MPI calls return the number of processes 38 being used and the rank of this process in the group. 39 */ 40 ierr = MPI_Comm_size(PETSC_COMM_WORLD,&size);CHKERRQ(ierr); 41 ierr = MPI_Comm_rank(PETSC_COMM_WORLD,&rank);CHKERRQ(ierr); 42 43 /* 44 Here we would like to print only one message that represents 45 all the processes in the group. We use PetscPrintf() with the 46 communicator PETSC_COMM_WORLD. Thus, only one message is 47 printed representng PETSC_COMM_WORLD, i.e., all the processors. 48 */ 49 ierr = PetscPrintf(PETSC_COMM_WORLD,"Number of processors = %d, rank = %d\n", size, rank);CHKERRQ(ierr); 50 51 /* 52 Always call PetscFinalize() before exiting a program. This routine 53 - finalizes the PETSc libraries as well as MPI 54 - provides summary and diagnostic information if certain runtime 55 options are chosen (e.g., -log_view). See PetscFinalize() 56 manpage for more information. 57 */ 58 ierr = PetscFinalize();if (ierr) return ierr; 59 60 ierr = MPI_Comm_free(&PETSC_COMM_WORLD);if (ierr) return ierr; 61 /* Since we initialized MPI, we must call MPI_Finalize() */ 62 ierr = MPI_Finalize(); 63 return ierr; 64 } 65 66 67 /*TEST 68 69 test: 70 nsize: 5 71 args: -options_left no 72 filter: sort -b | grep -v saws_port_auto_selectcd 73 filter_output: sort -b 74 75 TEST*/ 76