mpi simpson integration, scientific programming, exercise 1c

simpson1c.c

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

#define MASTER 0
#define REPETITIONS 10

double Function(double x);

int main(int argc, char *argv[]){
	int myrank, nprocs,a,b,i;
	long n, j;
	double times[REPETITIONS];
	double time, slowest, startInt, endInt,result,h,x,endresult;
	
	
  	MPI_Status recv_status;
	MPI_Request request;
	
  	MPI_Init(&argc, &argv);
  	MPI_Comm_rank(MPI_COMM_WORLD, &myrank);  
  	MPI_Comm_size(MPI_COMM_WORLD, &nprocs);
  
	if ( argc != 4 ){
    	printf("Usage: mpiexec -n nodecount simpson1c a b n\n\n");
		return 1;
    }
	
	a = atoi(argv[1]);
	b = atoi(argv[2]);
	n = atol(argv[3]);
	
	startInt = (double) ( b - a ) / nprocs * myrank + a;
	endInt = (double) ( b - a ) / nprocs * ( myrank + 1.0) + a;
	
	
	for ( i = 0 ; i < REPETITIONS ; ++i ){
		MPI_Barrier(MPI_COMM_WORLD);
		time = MPI_Wtime();
		
		h = ( ( endInt - startInt ) / n ) ; 
		x = startInt;
		result = Function(x); 
		x = x + h;
		for ( j=1l ; x < endInt ; ++j ){
			result = ( j % 2 == 0 ) ? result + 2 * Function(x) : result + 4 * Function(x);
			x = x + h;
		}
		result += Function(x);
		result = result / ( 3.0 ) * h;
		
		MPI_Reduce(&result,&endresult,1,MPI_DOUBLE,MPI_SUM,MASTER,MPI_COMM_WORLD);

		time = MPI_Wtime() - time;
		MPI_Barrier(MPI_COMM_WORLD); 
		MPI_Reduce(&time, &slowest, 1, MPI_DOUBLE, MPI_MAX, MASTER, MPI_COMM_WORLD);
		
		if (myrank == MASTER) {
	    	times[i]=slowest;
	   	}
	}
	
	if ( myrank == MASTER ){
		double min = times[0];
	   	for (int i = 1; i < REPETITIONS ; i++) {
			min = ( times[i] < min ) ? times[i] : min;
	   	}
		printf("%d;%ld;%f;%f\n", nprocs, n, min, endresult);
	}

  	MPI_Finalize();		
}

double Function(double x){
	double result = sqrt(1.0-x*x); 
	if ( isnan(result) ){ // sometimes encountert a problem with x=1.0 which resulted in minus zero.
		result = 0.0f;
	}
	return result;
}