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mpi.c
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mpi.c
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#include <stdio.h>
#include <assert.h>
#include <math.h>
#include <mpi.h>
const double PI = 3.1415926535897932;
const long STEP_NUM = 1070596096;
const double STEP_LENGTH = 1.0 / 1070596096;
int main (int argc, char* argv[])
{
double pi, sum = 0.0;
MPI_Init (&argc, &argv);
int rank, size;
// get process ID
MPI_Comm_rank (MPI_COMM_WORLD, &rank);
// get processes number
MPI_Comm_size (MPI_COMM_WORLD, &size);
// synchronize all processes and get the begin time
MPI_Barrier(MPI_COMM_WORLD);
if(rank == 0)
printf("\nStart calculating with %d processes...\n", size);
double startTime = MPI_Wtime();
double result = 0.0;
double x;
// each process will caculate a part of the sum
for (int i = rank * STEP_NUM / size; i < rank * STEP_NUM / size + STEP_NUM / size; i ++)
{
x = (i + 0.5) * STEP_LENGTH;
result += 1.0 / (1.0 + x * x);
}
// sum up all results
MPI_Reduce(&result, &sum, 1, MPI_DOUBLE, MPI_SUM, 0, MPI_COMM_WORLD);
// synchronize all processes and get the end time
MPI_Barrier(MPI_COMM_WORLD);
double endTime = MPI_Wtime();
// caculate and print PI
if (rank == 0)
{
pi = STEP_LENGTH * sum * 4;
printf("PI = %.16lf with error %.16lf\nTime elapsed : %lf seconds.\n\n", pi, fabs(pi - PI), (endTime - startTime));
assert(fabs(pi - PI) <= 0.001);
}
MPI_Finalize();
return 0;
}