c Compile with:
c Helios: mpif77 -o hello hello.f
c Hive, Portland: mpif77 -fc=pgf77 -o hello hello.f

 1    program test
 2    include 'mpif.h'
 3    integer ierr,id,lpname
 4    character*255 pname

 6    call MPI_INIT( ierr )
 7    call MPI_COMM_RANK(MPI_COMM_WORLD, id, ierr)
 8    call MPI_GET_PROCESSOR_NAME(pname,lpname,ierr)
 9    write(6,*)'Process',id,' running on ',pname(1:lpname)
 10   call MPI_FINALIZE(ierr)

 12   end

c Explanations:
c Line 1: Program name, standard Fortran
c Line 2: MPI header files contain the prototypes for MPI
c         functions/subroutines, as well as definitions of macros,
c         special constants, and datatypes used by MPI. An
c         appropriate "include" statement must appear in any
c         source file that contains MPI function calls or constants.
c Line 3: Definition of integers
c Line 4: Definition of characters
c Line 6: The first MPI routine called in any MPI program must be
c         the initialization routine MPI_INIT. This routine 
c         establishes the MPI environment, returning an error code
c         if there is a problem. MPI_INIT may be called only once
c         in any program! 
c Line 7: A processor can determine its rank in a communicator
c         (MPI_COMM_WORLD) with a call to MPI_COMM_RANK. The rank
c         is returned in 'id'. The error code 'ierr' returned is
c         MPI_SUCCESS if the routine ran successfully (that is,
c         the integer returned is equal to the pre-defined integer
c         constant MPI_SUCCESS). Thus, you can test for successful
c         operation with
c           if (ierr.eq.MPI_SUCCESS) THEN
c             ...routine ran correctly...
c           END IF
c Line 8: The name of the processor on which the present process
c         runs is returned in 'pname' and the
c         number of characters in the name of the processor is
c         returned in 'lpname'
c Line 9: Write out information
c Line 10: The last MPI routine called should be MPI_FINALIZE
c          which cleans up all MPI data structures, cancels
c          operations that never completed, etc. MPI_FINALIZE
c          must be called by all processes; if any one process
c          does not reach this statement, the program will appear
c          to hang. Once MPI_FINALIZE has been called, no other
c          MPI routines (including MPI_INIT) may be called.
c          The error code 'ierr' returned is
c          MPI_SUCCESS if the routine ran successfully (that is,
c          the integer returned is equal to the pre-defined integer
c          constant MPI_SUCCESS). Thus, you can test for successful
c          operation with
c           if (ierr.eq.MPI_SUCCESS) THEN
c             ...routine ran correctly...
c           END IF
c Line 12: End of program
c
c
c Each process executes the same code, including probing for
c its rank and processor name and printing the string. The order
c of the printed lines is essentially random! There is no intrinsic
c synchronization of operations on different processors. Each
c time the code is run, the order of the output lines may change.