feat: added mpi example code

setup_creators/mpi_example/pi_MPI.c

@@ -0,0 +1,61 @@
+#include <stdio.h>
+#include <math.h>
+#include "stdlib.h"
+#include "mpi.h"
+
+
+double f(double x){
+  return ( 4.0/(1.0 + x*x) );
+}
+
+
+int main(int argc,char *argv[])
+{
+
+  int myrank, size;
+
+  MPI_Init(&argc, &argv);
+  MPI_Comm_size(MPI_COMM_WORLD, &size);
+  MPI_Comm_rank(MPI_COMM_WORLD, &myrank);
+
+  long long int i, n;
+  double PI25DT = 3.141592653589793238462643;
+  double mypi, pi, h, mysum, x;
+
+
+
+  /* Argument handling from command line */
+  if( 2 == argc ){
+    n = atoll(argv[1]);
+  }else{
+    if( 0 == myrank ){
+      n = 10000000;
+      printf("Too many or no argument given; using n = %d instead.\n", n);
+    }
+  }
+
+
+  MPI_Bcast(&n, 1, MPI_LONG_LONG_INT, 0, MPI_COMM_WORLD);
+
+  h = 1.0/( (double)n );
+  mysum = 0.0;
+
+  for(i = myrank+1 ; i <= n ; i += size){
+    x = h*((double)i - 0.5);
+    mysum = mysum + f(x);
+  }
+
+  mypi = h*mysum;
+
+  MPI_Reduce(&mypi, &pi, 1, MPI_DOUBLE, MPI_SUM, 0, MPI_COMM_WORLD);
+
+  /* Output result if myrank==0 */
+  if( 0 == myrank ){
+    printf("\nUsing %d processes and the value n = %d.\n",size,n);
+    printf("Calculated pi: %.16f, with error %.16f\n\n", pi, fabs(pi - PI25DT));
+  }
+
+  MPI_Finalize();
+  return 0;
+}
+