From a053d8e4445609e854108c92cb56f39957ffcd5a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?David=20Doblas=20Jim=C3=A9nez?=
 <david.doblas-jimenez@xfel.eu>
Date: Mon, 12 Apr 2021 14:38:28 +0200
Subject: [PATCH] Ex. 1 ping_pong solution

---
 Exercises/ex_1/ping_pong/ping-pong.c | 58 ++++++++++++++++++++++++++++
 1 file changed, 58 insertions(+)
 create mode 100644 Exercises/ex_1/ping_pong/ping-pong.c

diff --git a/Exercises/ex_1/ping_pong/ping-pong.c b/Exercises/ex_1/ping_pong/ping-pong.c
new file mode 100644
index 0000000..b09ba41
--- /dev/null
+++ b/Exercises/ex_1/ping_pong/ping-pong.c
@@ -0,0 +1,58 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <mpi.h>
+
+#define MAX_I 20
+#define MAX_COUNT (1024 * 1024)
+
+double buf[MAX_COUNT];
+
+int main(int argc, char *argv[])  // ping pong
+{
+    int size, rank, partner, i, count, r, repetitions;
+    double time, bandwidth;
+    
+    MPI_Init(&argc, &argv);
+    MPI_Comm_size(MPI_COMM_WORLD, &size);
+    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
+
+    if (size != 2) {
+        fprintf(stderr, "comm_size != 2\n");
+        MPI_Abort(MPI_COMM_WORLD, 1);
+    }
+
+    if (rank == 0) {
+        puts("message size    number of         time    bandwidth");
+        puts("     [bytes]  repetitions         [us]       [MB/s]");
+        puts("---------------------------------------------------");
+    }
+                     
+    partner = 1 - rank;
+    count = 1;
+    repetitions = MAX_COUNT;
+
+    for (i = 0; i <= MAX_I; i++) {
+        time = MPI_Wtime();
+        for (r = 0; r < repetitions; r++) {
+            if (rank == 0) {
+                MPI_Send(buf, count, MPI_DOUBLE, partner, 0, MPI_COMM_WORLD);
+                MPI_Recv(buf, count, MPI_DOUBLE, partner, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
+            } else {
+                MPI_Recv(buf, count, MPI_DOUBLE, partner, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
+                MPI_Send(buf, count, MPI_DOUBLE, partner, 0, MPI_COMM_WORLD);
+            }
+        }
+        time = MPI_Wtime() - time;
+        time = time / (2.0 * repetitions);
+        time = 1e6 * time;  // micro-seconds
+        bandwidth = count * sizeof(double) / time;  // MByte/s
+
+        if (rank == 0)
+            printf("%12zd %12d %12.2f %12.2f\n", count * sizeof(double), repetitions, time, bandwidth);
+        count = count * 2;
+        repetitions = repetitions / 2;
+    }
+
+    MPI_Finalize();
+    return 0;
+}