使用MPI实现直方图：

#include
#include

//mpi
#include
//

#define MAXLINE 10000001

int main()
{
double *ptd;
char *ptc;
FILE *fp;
int i = 0;
double start, finish;
int count[10]={0};
int total_count[10]={0};
int num=0,source=0;

ptd = (double *)malloc(MAXLINE * sizeof(double));
ptc = (char *)malloc(10 * sizeof(char));

//mpi
int comm_sz;
int my_rank;
int local_num=0,local_a=0,local_b=0;
MPI_Init(NULL,NULL);
MPI_Comm_size(MPI_COMM_WORLD, &comm_sz);
MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);
//
if((fp = fopen("data.txt","r")) == NULL)
{
printf("Can't open \n");
exit(1);
}
i=0;
while(fgets(ptc, 10, fp) != NULL && ptc[0] != '\n' && i < MAXLINE)
{
ptd[i] = atof(ptc);
i++;
}

num = i;
local_b = num-1;

free(ptc);
if(fclose(fp)!=0)
{
fprintf(stderr,"Error closing file\n");
}

start = MPI_Wtime();
//mpi
local_num = num / comm_sz;
local_a = 0 + my_rank*local_num;
local_b = local_a + local_num-1;
for(i=local_a; i {
count[(int)ptd[i]]++;
}

if(my_rank != 0)
{
MPI_Send(count,10,MPI_INT,0,1,MPI_COMM_WORLD);
}
else
{
for(i=0;i<10;i++)
{
total_count[i] = count[i];
}
for(source=1;source {
MPI_Recv(count,10,MPI_INT,source,1,MPI_COMM_WORLD,MPI_STATUS_IGNORE);
for(i=0;i<10;i++)
{
total_count[i] += count[i];
}
}
}

finish = MPI_Wtime();
if(my_rank==0)
{
for(i=0;i<10;i++)
{
printf("%d<=x<%d: %d条\n",i,i+1,total_count[i]);
}
printf("It cost : %f ms\n",(finish-start)*1000.0);

}
/*
for(i=0;i<10;i++)
{
printf("%d<=x<%d: %d条\n",i,i+1,count[i]);
}
printf("Proc %d cost : %f ms\n",my_rank,(finish-start)*1000.0);
*/
MPI_Finalize();
//
free(ptd);
return 0;
}