1c4762a1bSJed Brown! 2c4762a1bSJed Brown! This introductory example illustrates running PETSc on a subset 3c4762a1bSJed Brown! of processes 4c4762a1bSJed Brown! 5c4762a1bSJed Brown! ----------------------------------------------------------------------- 6c4762a1bSJed Brown 7c4762a1bSJed Brownprogram main 8c4762a1bSJed Brown#include <petsc/finclude/petscsys.h> 98c8af28eSPedro Ricardo C. Souza use petscmpi ! or mpi or mpi_f08 10c4762a1bSJed Brown use petscsys 11c4762a1bSJed Brown implicit none 12c4762a1bSJed Brown 13c4762a1bSJed Brown PetscErrorCode ierr 144a713726SSatish Balay PetscMPIInt rank, size, zero, two 15c4762a1bSJed Brown 16c4762a1bSJed Brown! We must call MPI_Init() first, making us, not PETSc, responsible 17c4762a1bSJed Brown! for MPI 18c4762a1bSJed Brown 19f8402805SBarry Smith PetscCallMPIA(MPI_Init(ierr)) 20c4762a1bSJed Brown 21c4762a1bSJed Brown! We can now change the communicator universe for PETSc 22c4762a1bSJed Brown 234a713726SSatish Balay zero = 0 24c4762a1bSJed Brown two = 2 25f8402805SBarry Smith PetscCallMPIA(MPI_Comm_rank(MPI_COMM_WORLD, rank, ierr)) 26f8402805SBarry Smith PetscCallMPIA(MPI_Comm_split(MPI_COMM_WORLD, mod(rank, two), zero, PETSC_COMM_WORLD, ierr)) 27c4762a1bSJed Brown 28c4762a1bSJed Brown! Every PETSc routine should begin with the PetscInitialize() 29c4762a1bSJed Brown! routine. 30c4762a1bSJed Brown 31d8606c27SBarry Smith PetscCallA(PetscInitialize(ierr)) 32c4762a1bSJed Brown 33c4762a1bSJed Brown! The following MPI calls return the number of processes being used 34c4762a1bSJed Brown! and the rank of this process in the group. 35c4762a1bSJed Brown 36f8402805SBarry Smith PetscCallMPIA(MPI_Comm_size(PETSC_COMM_WORLD, size, ierr)) 37f8402805SBarry Smith PetscCallMPIA(MPI_Comm_rank(PETSC_COMM_WORLD, rank, ierr)) 38c4762a1bSJed Brown 39c4762a1bSJed Brown! Here we would like to print only one message that represents all 40c4762a1bSJed Brown! the processes in the group. 41*4820e4eaSBarry Smith if (rank == 0) write (6, 100) size, rank 42c4762a1bSJed Brown100 format('No of Procs = ', i4, ' rank = ', i4) 43c4762a1bSJed Brown 44c4762a1bSJed Brown! Always call PetscFinalize() before exiting a program. This 45c4762a1bSJed Brown! routine - finalizes the PETSc libraries as well as MPI - provides 46c4762a1bSJed Brown! summary and diagnostic information if certain runtime options are 47c4762a1bSJed Brown! chosen (e.g., -log_view). See PetscFinalize() manpage for more 48c4762a1bSJed Brown! information. 49c4762a1bSJed Brown 50f8402805SBarry Smith PetscCallA(PetscFinalize(ierr)) 51f8402805SBarry Smith PetscCallMPIA(MPI_Comm_free(PETSC_COMM_WORLD, ierr)) 52c4762a1bSJed Brown 53c4762a1bSJed Brown! Since we initialized MPI, we must call MPI_Finalize() 54c4762a1bSJed Brown 55f8402805SBarry Smith PetscCallMPIA(MPI_Finalize(ierr)) 56c4762a1bSJed Brownend 57c4762a1bSJed Brown 58c4762a1bSJed Brown! 59c4762a1bSJed Brown!/*TEST 60c4762a1bSJed Brown! 61c4762a1bSJed Brown! test: 62c4762a1bSJed Brown! 63c4762a1bSJed Brown!TEST*/ 64