Ex. 1 master_worker solution

Exercises/ex_2/ring.c

@@ -0,0 +1,32 @@
+#include <stdio.h>
+#include <mpi.h>
+
+int main(int argc, char *argv[])  // ring
+{
+    int size, rank;
+    int partner_left, partner_right;
+    int sum, sbuf, rbuf;
+
+    MPI_Init(&argc, &argv);
+    MPI_Comm_size(MPI_COMM_WORLD, &size);
+    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
+
+    partner_left  = (rank - 1 + size) % size;
+    partner_right = (rank + 1) % size;
+
+    sum = 0;
+    sbuf = rank;
+
+    do {
+	MPI_Sendrecv(&sbuf, 1, MPI_INT, partner_right, 0,
+		     &rbuf, 1, MPI_INT, partner_left, 0, 
+                     MPI_COMM_WORLD, MPI_STATUS_IGNORE);
+	sum += rbuf;
+	sbuf = rbuf;
+    } while (rbuf != rank);
+  
+    printf("%d %d\n", rank, sum);
+    
+    MPI_Finalize();
+    return 0;
+}