- Convert MPI_Init(NULL, NULL) to MPI_Init(&argc, &argv) because

apparently some people are using these examples to test other MPI's,
  and some of those MPI's don't handle MPI_Init(NULL, NULL) properly.
  :-)
- Add comments and a print statement to the f90 example to make it
  like the others.

This commit was SVN r11123.

examples/hello_c.c

@@ -14,7 +14,7 @@ int main(int argc, char* argv[])
 {
     int rank, size;
 
-    MPI_Init(NULL, NULL);
+    MPI_Init(&argc, &argv);
     MPI_Comm_rank(MPI_COMM_WORLD, &rank);
     MPI_Comm_size(MPI_COMM_WORLD, &size);
     printf("Hello, world, I am %d of %d\n", rank, size);

examples/ring_c.c

@@ -16,7 +16,7 @@ int main(int argc, char *argv[])
 
     /* Start up MPI */
 
-    MPI_Init(NULL, NULL);
+    MPI_Init(&argc, &argv);
     MPI_Comm_rank(MPI_COMM_WORLD, &rank);
     MPI_Comm_size(MPI_COMM_WORLD, &size);
  

examples/ring_f90.f90

@@ -11,21 +11,36 @@ program ring
   implicit none
   integer :: rank, size, tag, next, from, message, ierr
 
+! Start up MPI
+
   call MPI_INIT(ierr)
   call MPI_COMM_RANK(MPI_COMM_WORLD, rank, ierr)
   call MPI_COMM_SIZE(MPI_COMM_WORLD, size, ierr)
 
+! Calculate the rank of the next process in the ring.  Use the modulus
+! operator so that the last process "wraps around" to rank zero.
+
   tag = 201
   next = mod((rank + 1), size)
   from = mod((rank + size - 1), size)
       
+! If we are the "master" process (i.e., MPI_COMM_WORLD rank 0), put
+! the number of times to go around the ring in the message.
+
   if (rank .eq. 0) then
      message = 10
 
      print *, 'Process 0 sending ', message, ' to ',  next
      call MPI_SEND(message, 1, MPI_INTEGER, next, tag, MPI_COMM_WORLD, ierr)
+     print *, 'Process 0 sent to ', next
   endif
 
+! Pass the message around the ring.  The exit mechanism works as
+! follows: the message (a positive integer) is passed around the ring.
+! Each time it passes rank 0, it is decremented.  When each processes
+! receives a message containing a 0 value, it passes the message on to
+! the next process and then quits.  By passing the 0 message first,
+! every process gets the 0 message and can quit normally.
 
 10 call MPI_RECV(message, 1, MPI_INTEGER, from, tag, MPI_COMM_WORLD, &
         MPI_STATUS_IGNORE, ierr)
@@ -43,11 +58,16 @@ program ring
   endif
   goto 10
 
+! The last process does one extra send to process 0, which needs to be
+! received before the program can exit
+
  20 if (rank .eq. 0) then
      call MPI_RECV(message, 1, MPI_INTEGER, from, tag, MPI_COMM_WORLD, &
           MPI_STATUS_IGNORE, ierr)
   endif
 
+! All done
+
   call MPI_FINALIZE(ierr)
 end program