Parallel Implementation

/* Let the system do what it needs to start up MPI*/

MPI_Init(&argc, &argv);

/* Get my process rank */

MPI_Comm_rank(MPI_COMM_WORLD,

&my_rank);

/* Find out how many processes are being used */

MPI_Comm_size(MPI_COMM_WORLD, &p);

h = (b-a)/n; /* h is the same for all processes */

local_n = n/p; /* So is the number of trapezoids */

/* Length of each process' interval of

* integration = local_n*h. So my interval

* starts at: */

local_a = a + my_rank*local_n*h;

local_b = local_a + local_n*h;

integral = Trap(local_a, local_b, local_n, h);

/* sum the integrals calculated by each process */

if (my_rank == 0) {

total = integral;

for (source = 1; source < p; source++) {

MPI_Recv(&integral, 1, MPI_FLOAT, source,

tag, MPI_COMM_WORLD, &status);

total = total + integral;

}

} else {

MPI_Send(&integral, 1, MPI_FLOAT, dest,

tag, MPI_COMM_WORLD);

}

/* Print the result */

if (my_rank == 0) {

printf("With n = %d trapezoids, our estimate\n",

n);

printf("of the integral from %f to %f = %f\n",

a, b, total);

}

/* Shut down MPI */

MPI_Finalize();

} /* main */

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