1c4762a1bSJed Brown! 2c4762a1bSJed Brown! This introductory example illustrates running PETSc on a subset 3c4762a1bSJed Brown! of processes 4c4762a1bSJed Brown! 5c4762a1bSJed Brown!/*T 6c4762a1bSJed Brown! Concepts: introduction to PETSc; 7c4762a1bSJed Brown! Concepts: process^subset set PETSC_COMM_WORLD 8c4762a1bSJed Brown! Processors: 2 9c4762a1bSJed Brown!T*/ 10c4762a1bSJed Brown! ----------------------------------------------------------------------- 11c4762a1bSJed Brown 12c4762a1bSJed Brown program main 13c4762a1bSJed Brown#include <petsc/finclude/petscsys.h> 14c4762a1bSJed Brown use petscsys 15c4762a1bSJed Brown implicit none 16c4762a1bSJed Brown 17c4762a1bSJed Brown PetscErrorCode ierr 18*4a713726SSatish Balay PetscMPIInt rank, size, zero, two 19c4762a1bSJed Brown 20c4762a1bSJed Brown! We must call MPI_Init() first, making us, not PETSc, responsible 21c4762a1bSJed Brown! for MPI 22c4762a1bSJed Brown 23c4762a1bSJed Brown call MPI_Init(ierr) 24c4762a1bSJed Brown if (ierr .ne. 0) then 25c4762a1bSJed Brown print*,'Unable to initialize MPI' 26c4762a1bSJed Brown stop 27c4762a1bSJed Brown endif 28c4762a1bSJed Brown 29c4762a1bSJed Brown! We can now change the communicator universe for PETSc 30c4762a1bSJed Brown 31*4a713726SSatish Balay zero = 0 32c4762a1bSJed Brown two = 2 33c4762a1bSJed Brown call MPI_Comm_rank(MPI_COMM_WORLD,rank,ierr) 34*4a713726SSatish Balay call MPI_Comm_split(MPI_COMM_WORLD,mod(rank,two),zero,PETSC_COMM_WORLD,ierr) 35c4762a1bSJed Brown 36c4762a1bSJed Brown! Every PETSc routine should begin with the PetscInitialize() 37c4762a1bSJed Brown! routine. 38c4762a1bSJed Brown 39c4762a1bSJed Brown call PetscInitialize(PETSC_NULL_CHARACTER,ierr) 40c4762a1bSJed Brown if (ierr .ne. 0) then 41c4762a1bSJed Brown print*,'Unable to initialize PETSc' 42c4762a1bSJed Brown stop 43c4762a1bSJed Brown endif 44c4762a1bSJed Brown 45c4762a1bSJed Brown! The following MPI calls return the number of processes being used 46c4762a1bSJed Brown! and the rank of this process in the group. 47c4762a1bSJed Brown 48c4762a1bSJed Brown call MPI_Comm_size(PETSC_COMM_WORLD,size,ierr);CHKERRA(ierr) 49c4762a1bSJed Brown call MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr);CHKERRA(ierr) 50c4762a1bSJed Brown 51c4762a1bSJed Brown 52c4762a1bSJed Brown! Here we would like to print only one message that represents all 53c4762a1bSJed Brown! the processes in the group. 54c4762a1bSJed Brown if (rank .eq. 0) write(6,100) size,rank 55c4762a1bSJed Brown 100 format('No of Procs = ',i4,' rank = ',i4) 56c4762a1bSJed Brown 57c4762a1bSJed Brown! Always call PetscFinalize() before exiting a program. This 58c4762a1bSJed Brown! routine - finalizes the PETSc libraries as well as MPI - provides 59c4762a1bSJed Brown! summary and diagnostic information if certain runtime options are 60c4762a1bSJed Brown! chosen (e.g., -log_view). See PetscFinalize() manpage for more 61c4762a1bSJed Brown! information. 62c4762a1bSJed Brown 63c4762a1bSJed Brown call PetscFinalize(ierr) 64c4762a1bSJed Brown call MPI_Comm_free(PETSC_COMM_WORLD,ierr) 65c4762a1bSJed Brown 66c4762a1bSJed Brown! Since we initialized MPI, we must call MPI_Finalize() 67c4762a1bSJed Brown 68c4762a1bSJed Brown call MPI_Finalize(ierr) 69c4762a1bSJed Brown end 70c4762a1bSJed Brown 71c4762a1bSJed Brown! 72c4762a1bSJed Brown!/*TEST 73c4762a1bSJed Brown! 74c4762a1bSJed Brown! test: 75c4762a1bSJed Brown! 76c4762a1bSJed Brown!TEST*/ 77