Changes between Version 1 and Version 2 of mpich/2008-07-20_YM_MPI_Course

Timestamp:

Jul 20, 2008, 5:37:18 PM (16 years ago)

Author:

jazz

Comment:

--

mpich/2008-07-20_YM_MPI_Course

@@ -253 +253 @@
 {{{
 /* Program:
- *   讓 node 0 可以接受來自任何 node 的訊息，每個 node 將訊息標上不同 tag 後傳給 node 0
+ *   mpich_example 內建範例，計算 pi 。
  * History:
- *   2008-06-24 BETA
- */
-
+ *   2008-04-11 BETA
+ *   2008-06-19 增加可重複輸入欲計算之精準度
+ *   2008-06-23 加入 MPI_Barrier 以確保每個 node 在接受 n 後才執行
+ * /
+
+#include "mpi.h"
 #include <stdio.h>
-#include <mpi.h>
-
-main (int argc, char **argv)
+#include <math.h>
+#include <time.h>
+
+double f( double );
+double f( double a )
 {
-  int numprocs, myrank, i=0, buf;
-  MPI_Status status;
-  MPI_Init(&argc, &argv);
-  MPI_Comm_size(MPI_COMM_WORLD, &numprocs);
-  MPI_Comm_rank(MPI_COMM_WORLD, &myrank);
-
-  /* 除了 Node 0 以外的所有 node 都要送 5 個訊息給 node 0 ， 將 i 當成 tag 送出 */
-  if (myrank > 0)
-  {
-    for(i = 0; i < 5; i++)
+    return (4.0 / (1.0 + a*a));
+}
+
+int main( int argc, char *argv[])
+{
+    int done = 0, n, myid, numprocs, i=0;
+    double PI25DT = 3.141592653589793238462643;
+    double mypi, pi, h, sum, x;
+    double startwtime = 0.0, endwtime;
+    int  namelen;
+    char processor_name[MPI_MAX_PROCESSOR_NAME];
+    MPI_Init(&argc,&argv);
+    MPI_Comm_size(MPI_COMM_WORLD,&numprocs);
+    MPI_Comm_rank(MPI_COMM_WORLD,&myid);
+    MPI_Get_processor_name(processor_name,&namelen);
+    fprintf(stderr,"Process %d on %s\n",
+            myid, processor_name);
+    n = 0;
+    while (!done)
     {
-      buf = myrank * 100 + i;
-      MPI_Send(&buf, 1, MPI_INT, 0, i, MPI_COMM_WORLD);
+        /* 由 node 0 將使用者輸入的值送給其它的 node  */
+        if (myid == 0)
+        {
+            printf("Enter the number of intervals: (0 quits) ");
+            scanf("%d", &n);
+            startwtime = MPI_Wtime();
+        }
+
+        /* 這非常重要，所有的 node 必需在此同步，才可以收到使用者輸入的 n */
+        MPI_Barrier(MPI_COMM_WORLD);
+
+        /* 將 n 送給其它的 node  */
+        MPI_Bcast(&n, 1, MPI_INT, 0, MPI_COMM_WORLD);
+        if (n == 0)
+            done = 1;
+        else
+        {
+
+            /* 此為計算 pi 的演算法 */
+            h   = 1.0 / (double) n;
+            sum = 0.0;
+            for (i = myid + 1; i <= n; i += numprocs)
+            {
+                x = h * ((double)i - 0.5);
+                sum += f(x);
+            }
+            mypi = h * sum;
+
+            /* 將算完的結果傳給 node 0 加總 */
+            MPI_Reduce(&mypi, &pi, 1, MPI_DOUBLE, MPI_SUM, 0, MPI_COMM_WORLD);
+            if (myid == 0)
+            {
+                printf("pi is approximately %.16f, Error is %.16f\n",
+                       pi, fabs(pi - PI25DT));
+                endwtime = MPI_Wtime();
+                printf("wall clock time = %f\n",
+                       endwtime-startwtime);
+            }
+        }
     }
-  }
-  if (myrank == 0)
-  {
-    for (i = 0; i < 5*(numprocs-1); i++)
-    {
-
-      /* MPI_ANY_SOURCE 接收來自任何 node ， MPI_ANY_TAG 接收來自任何 tag */
-      MPI_Recv(&buf, 1, MPI_INT, MPI_ANY_SOURCE, MPI_ANY_TAG, MPI_COMM_WORLD, &status);
-      printf("[Node %d][Tag %d] => %d\n", status.MPI_SOURCE, status.MPI_TAG, buf);
-    }
-  }
-  MPI_Finalize();
+    MPI_Finalize();
+    return 0;
 }
 }}}