! ! This introductory example illustrates running PETSc on a subset ! of processes ! !/*T ! Concepts: introduction to PETSc; ! Concepts: process^subset set PETSC_COMM_WORLD ! Processors: 2 !T*/ ! ----------------------------------------------------------------------- program main #include use petscsys implicit none PetscErrorCode ierr PetscMPIInt rank, size, two ! We must call MPI_Init() first, making us, not PETSc, responsible ! for MPI call MPI_Init(ierr) if (ierr .ne. 0) then print*,'Unable to initialize MPI' stop endif ! We can now change the communicator universe for PETSc two = 2 call MPI_Comm_rank(MPI_COMM_WORLD,rank,ierr) call MPI_Comm_split(MPI_COMM_WORLD,mod(rank,two),0,PETSC_COMM_WORLD,ierr) ! Every PETSc routine should begin with the PetscInitialize() ! routine. call PetscInitialize(PETSC_NULL_CHARACTER,ierr) if (ierr .ne. 0) then print*,'Unable to initialize PETSc' stop endif ! The following MPI calls return the number of processes being used ! and the rank of this process in the group. call MPI_Comm_size(PETSC_COMM_WORLD,size,ierr);CHKERRA(ierr) call MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr);CHKERRA(ierr) ! Here we would like to print only one message that represents all ! the processes in the group. if (rank .eq. 0) write(6,100) size,rank 100 format('No of Procs = ',i4,' rank = ',i4) ! Always call PetscFinalize() before exiting a program. This ! routine - finalizes the PETSc libraries as well as MPI - provides ! summary and diagnostic information if certain runtime options are ! chosen (e.g., -log_view). See PetscFinalize() manpage for more ! information. call PetscFinalize(ierr) call MPI_Comm_free(PETSC_COMM_WORLD,ierr) ! Since we initialized MPI, we must call MPI_Finalize() call MPI_Finalize(ierr) end ! !/*TEST ! ! test: ! !TEST*/