parallelpisolution.c

并行计算,用于计算PI的程序实例,parallel programing

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

void main(int argc, char *argv[])
{
	int		NumIntervals	= 0;	//num intervals in the domain [0,1] of F(x)= 4 / (1 + x*x)
	double	IntervalWidth	= 0.0;	//width of intervals
	double  IntervalLength  = 0.0;	//length of intervals
	double	IntrvlMidPoint	= 0.0;	//x mid point of interval
	int		Interval		= 0;	//loop counter
	int		done			= 0;	//flag
	double	MyPI			= 0.0;	//storage for PI approximation results
	double	ReferencePI		= 3.141592653589793238462643; //ref value of PI for comparison
	double  PI;
	char	processor_name[MPI_MAX_PROCESSOR_NAME];
	char	(*all_proc_names)[MPI_MAX_PROCESSOR_NAME];
	int		numprocs;
	int		MyID;
	int		namelen;
	int		proc = 0;

	MPI_Init(&argc,&argv);
	MPI_Comm_size(MPI_COMM_WORLD,&numprocs);
	MPI_Comm_rank(MPI_COMM_WORLD,&MyID);
	MPI_Get_processor_name(processor_name,&namelen);

	all_proc_names = malloc(numprocs * MPI_MAX_PROCESSOR_NAME);

	MPI_Gather(processor_name, MPI_MAX_PROCESSOR_NAME, MPI_CHAR, all_proc_names, MPI_MAX_PROCESSOR_NAME, MPI_CHAR, 0, MPI_COMM_WORLD);
	for (proc=0; proc < numprocs; ++proc)
		printf("Process %d on %s\n", proc, all_proc_names[proc]);

	while (!done) //loops until done == 0
	{
		IntervalLength = 0.0;
		if (MyID == 0){ 
			printf("\nEnter the number of intervals: (0 quits) ");fflush(stdout);
			scanf_s("%d",&NumIntervals);
		}

		MPI_Bcast(&NumIntervals, 1, MPI_INT, 0, MPI_COMM_WORLD);   /* send number of intervals to all procs */

		if (NumIntervals == 0)
			done = 1;   //exit if number of intervals = 0  
		else
		{
			//approximate the value of PI
			IntervalWidth   = 1.0 / (double) NumIntervals;           

			for (Interval = MyID + 1; Interval <= NumIntervals; Interval += numprocs){
				IntrvlMidPoint = IntervalWidth * ((double)Interval - 0.5);
				IntervalLength += (4.0 / (1.0 + IntrvlMidPoint*IntrvlMidPoint));
			}

			MyPI = IntervalWidth * IntervalLength;

			MPI_Reduce(&MyPI, &PI, 1, MPI_DOUBLE, MPI_SUM, 0, MPI_COMM_WORLD);

			//report approximation
			if (MyID == 0){
			printf("PI is approximately %.16f, Error is %.16f\n",
					PI, fabs(PI - ReferencePI));
			}
		}
	}
	MPI_Finalize();
}