integral_cte.c

#include <mpi.h>
#include <math.h>
#include <stdio.h>

float fct(float x)
{
      return (x/sin(x))*(x/sin(x));
}

float integral(float a, int n, float h);

void main(argc,argv)
int argc;
char *argv[];
{
      int n, p, i, j, ierr,num,my_id;
      float h, result, a, b, pi;
      float my_a, my_range;
      double start = 0.0, end;

      int myid, source, dest, tag;
      MPI_Status status;
      float my_result;

      pi = acos(-1.0);  /* = 3.14159... */
      a = 0.;           /* lower limit of integration */
      b = pi*1./2.;     /* upper limit of integration */
      n = 100000;          /* number of increment within each process */
      dest = 0;         /* define the process that computes the final result */
      tag = 123;        /* set the tag to identify this particular job */

      /* Starts MPI processes ... */

      MPI_Init(&argc,&argv);              /* starts MPI */
      MPI_Comm_rank(MPI_COMM_WORLD, &myid);  /* get current process id */
      MPI_Comm_size(MPI_COMM_WORLD, &p);     /* get number of processes */

      if (my_id == 0)
        start = MPI_Wtime();

      h = (b-a)/n;    /* length of increment */
      num = n/p;	/* number of intervals calculated by each process*/
      
      my_range = (b-a)/p;
      my_a = a + myid*my_range;
      my_result = integral(my_a,num,h);

      if(myid == 0) {
        result = my_result;
        for (i=1;i<p;i++) {
          source = i;           /* MPI process number range is [0,p-1] */
          MPI_Recv(&my_result, 1, MPI_REAL, source, tag,
                        MPI_COMM_WORLD, &status);
          result += my_result;
        }
        end = MPI_Wtime();
        printf("%f",result);
        printf(",%e\n", end-start);
      }
      else
        MPI_Send(&my_result, 1, MPI_REAL, dest, tag,
                      MPI_COMM_WORLD);      /* send my_result to intended dest.
                      */
      MPI_Finalize();                       /* let MPI finish up ... */
}

float integral(float a, int n, float h)
{
      int j;
      float h2, aij, integ;

      integ = 0.0;                 /* initialize integral */
      h2 = h/2.;
      for (j=0;j<n;j++) {             /* sum over all "j" integrals */
        aij = a + j*h;        /* lower limit of "j" integral */
        integ += fct(aij+h2)*h;
      }
      return (integ);
}