使用MPI_Send和MPI_Recv实现MPI_Reduce会导致错误的结果
我正在开发一个程序,它使用使用MPI_Send和MPI_Recv实现MPI_Reduce会导致错误的结果,c,performance,parallel-processing,mpi,hpc,C,Performance,Parallel Processing,Mpi,Hpc,我正在开发一个程序,它使用MPI\u Send()和MPI\u Recv()替换MPI\u Reduce() 我得到了所有要运行的东西,除了代码的最后一部分,它给出了PI近似值、错误和运行时间。我收到后也没有得到正确的和值 我相信在MPI\u Recv()。运行此程序时,我只使用2个处理器。当使用MPI\u Reduce时,如果PI未初始化为某个值,程序运行正常 #include "mpi.h" #include <stdio.h> #include <ma
MPI\u Send()
和MPI\u Recv()
替换MPI\u Reduce()
我得到了所有要运行的东西,除了代码的最后一部分,它给出了PI近似值、错误和运行时间。我收到后也没有得到正确的和值
我相信在MPI\u Recv()。运行此程序时,我只使用2个处理器。当使用MPI\u Reduce
时,如果PI未初始化为某个值,程序运行正常
#include "mpi.h"
#include <stdio.h>
#include <math.h>
int main( int argc, char *argv[])
{
int n, i;
double PI25DT = 3.141592653589793238462643;
double pi, h, sum, x;
int size, rank;
double startTime, endTime;
/* Initialize MPI and get number of processes and my number or rank*/
MPI_Init(&argc,&argv);
MPI_Comm_size(MPI_COMM_WORLD,&size);
MPI_Comm_rank(MPI_COMM_WORLD,&rank);
/* Processor zero sets the number of intervals and starts its clock*/
if (rank==0)
{
n=600000000;
startTime=MPI_Wtime();
for (int i = 0; i < size; i++) {
if (i != rank) {
MPI_Send(&n, 1, MPI_INT, i, 0, MPI_COMM_WORLD);
}
}
}
/* Broadcast number of intervals to all processes */
else
{
MPI_Recv(&n, 1, MPI_INT, 0, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
}
/* Calculate the width of intervals */
h = 1.0 / (double) n;
/* Initialize sum */
sum = 0.0;
/* Step over each inteval I own */
for (i = rank+1; i <= n; i += size)
{
/* Calculate midpoint of interval */
x = h * ((double)i - 0.5);
/* Add rectangle's area = height*width = f(x)*h */
sum += (4.0/(1.0+x*x))*h;
}
/* Get sum total on processor zero */
//MPI_Reduce(&sum,&pi,1,MPI_DOUBLE,MPI_SUM,0,MPI_COMM_WORLD);
MPI_Send(&sum, 1, MPI_DOUBLE, 0, 0, MPI_COMM_WORLD);
MPI_Send(&pi, 1, MPI_SUM, 0, 0, MPI_COMM_WORLD);
if (rank == 0)
{
double total_sum = 0;
for (int i = 0; i < size; i++)
{
MPI_Recv(&sum, 1, MPI_DOUBLE, i, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
MPI_Recv(&pi, 1, MPI_SUM, i, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
total_sum += sum;
printf("Total Sum is %lf\n", total_sum);
}
}
/* Print approximate value of pi and runtime*/
if (rank==0)
{
printf("pi is approximately %.16f, Error is %e\n",
pi, fabs(pi - PI25DT));
endTime=MPI_Wtime();
printf("runtime is=%.16f",endTime-startTime);
}
MPI_Finalize();
return 0;
}
#包括“mpi.h”
#包括
#包括
int main(int argc,char*argv[])
{
int n,i;
双PI25DT=3.141592653589793238462643;
双π,h,和,x;
整数大小、等级;
双开始时间,结束时间;
/*初始化MPI并获取进程数和我的编号或排名*/
MPI_Init(&argc,&argv);
MPI_通信大小(MPI_通信世界和大小);
MPI通信等级(MPI通信世界和等级);
/*处理器zero设置间隔数并启动其时钟*/
如果(秩==0)
{
n=600000000;
startTime=MPI_Wtime();
对于(int i=0;i
及
错误,应作为第三个参数MPI\u数据类型
而不是MPI\u OP
(即MPI\u总和
)
但看看你的代码,你真正想做的是用以下方法替换这些调用:
double pi = sum;
if (myid != 0) {
MPI_Send(&sum, 1, MPI_DOUBLE, 0, 0, MPI_COMM_WORLD);
}
else {
for (int i = 1; i < numprocs; i++) {
MPI_Recv(&value, 1, MPI_DOUBLE, i, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
pi += value;
}
}
输出(2个过程):
MPI_Recv(&pi, 1, MPI_SUM, i, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
^^^^^^^
double pi = sum;
if (myid != 0) {
MPI_Send(&sum, 1, MPI_DOUBLE, 0, 0, MPI_COMM_WORLD);
}
else {
for (int i = 1; i < numprocs; i++) {
MPI_Recv(&value, 1, MPI_DOUBLE, i, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
pi += value;
}
}
#include "mpi.h"
#include <stdio.h>
#include <math.h>
int main( int argc, char *argv[])
{
int n, i;
double PI25DT = 3.141592653589793238462643;
double h, sum, x;
int numprocs, myid;
double startTime, endTime;
/* Initialize MPI and get number of processes and my number or rank*/
MPI_Init(&argc,&argv);
MPI_Comm_size(MPI_COMM_WORLD,&numprocs);
MPI_Comm_rank(MPI_COMM_WORLD,&myid);
/* Processor zero sets the number of intervals and starts its clock*/
if (myid==0) {
n=600000000;
startTime=MPI_Wtime();
for (int i = 0; i < numprocs; i++) {
if (i != myid) {
MPI_Send(&n, 1, MPI_INT, i, 0, MPI_COMM_WORLD);
}
}
}
else {
MPI_Recv(&n, 1, MPI_INT, 0, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
}
/* Calculate the width of intervals */
h = 1.0 / (double) n;
/* Initialize sum */
sum = 0.0;
/* Step over each inteval I own */
for (i = myid+1; i <= n; i += numprocs) {
/* Calculate midpoint of interval */
x = h * ((double)i - 0.5);
/* Add rectangle's area = height*width = f(x)*h */
sum += (4.0/(1.0+x*x))*h;
}
/* Get sum total on processor zero */
//MPI_Reduce(&sum,&pi,1,MPI_DOUBLE,MPI_SUM,0,MPI_COMM_WORLD);
double value = 0;
double pi = sum;
if (myid != 0) {
MPI_Send(&sum, 1, MPI_DOUBLE, 0, 0, MPI_COMM_WORLD);
}
else {
for (int i = 1; i < numprocs; i++) {
MPI_Recv(&value, 1, MPI_DOUBLE, i, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
pi += value;
}
}
/* Print approximate value of pi and runtime*/
if (myid==0) {
printf("pi is approximately %.16f, Error is %e\n",
pi, fabs(pi - PI25DT));
endTime=MPI_Wtime();
printf("runtime is=%.16f",endTime-startTime);
}
MPI_Finalize();
return 0;
}
pi is approximately 3.1415926535898993, Error is 1.061373e-13
runtime is=1.3594319820404053