該程序通過將隨機「飛鏢」(採樣點)投擲到長方形棋盤內的圓形或半徑= 1內來估計Pi。使用關係當多個進程初始化時,爲什麼這個程序會卡住?
Area of circle/Area of Square = Pi/4
,我們可以使用相同的關係估計丕表示
Darts Inside Circle/Darts Outside Circle = Pi/4
,當我在一個#define
指定NDARTS
程序工作正常。然而,當我指定NDARTS作爲一種價值that's read via scanf and then broadcasted,它神祕地獲取在超過一個過程是通過指定的mpirun卡:
mpirun -np 1 ./pi_montecarlo.x
Monte Carlo Method to estimate Pi
Introduce Number of Darts
10000
Number of processes: 1
Number of darts: 10000
Known value of PI : 3.1415926535
Estimated Value of PI : 3.1484000000
Error Percentage : 0.21668457
Time : 0.00060296
mpirun -np 2 ./pi_montecarlo.x
Monte Carlo Method to estimate Pi
Introduce Number of Darts
10000
Number of processes: 2
Number of darts: 10000
^困在這裏。
爲什麼?這是一些特定於mpi實現的問題嗎?我應該嘗試其他MPI實現嗎(我想我正在運行lam)?你可以在自己的盒子上至少運行2個進程嗎?
/*
mpicc -g -Wall -lm pi_montecarlo3.c -o pi_montecarlo.x
mpirun -np 4 ./pi_montecarlo.x
*/
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <time.h>
#include <mpi.h>
#define MASTER 0
#define PI 3.1415926535
double pseudo_random (double a, double b) {
double r;
r = ((b-a) * ((double) rand()/(double) RAND_MAX)) +a;
return r;
}
int main(int argc, char*argv[]){
long long int NDARTS;
int proc_id,
n_procs,
llimit,
ulimit,
n_circle,
i;
double pi_current,
pi_sum,
x,
y,
z,
error,
start_time,
end_time;
struct timeval stime;
llimit = -1;
ulimit = 1;
n_circle =0;
MPI_Init(&argc, &argv);
MPI_Comm_rank (MPI_COMM_WORLD, &proc_id);
MPI_Comm_size (MPI_COMM_WORLD, &n_procs);
if (proc_id == MASTER){
printf("\nMonte Carlo Method to estimate Pi \n\n");
printf("Introduce Number of Darts \n");
scanf("%lld",&NDARTS);
printf(" Number of processes: %d \n", n_procs);
printf(" Number of darts: %lld \n", NDARTS);
MPI_Bcast(&NDARTS, 1, MPI_LONG_LONG_INT, 0, MPI_COMM_WORLD);
start_time = MPI_Wtime();
}
gettimeofday(&stime, NULL);
srand(stime.tv_usec * stime.tv_usec * stime.tv_usec * stime.tv_usec);
for (i=1; i<=NDARTS;i++){
x = pseudo_random(llimit, ulimit);
y = pseudo_random(llimit, ulimit);
z = pow(x,2) + pow(y,2);
if (z<=1.0){
n_circle++;
}
}
pi_current = 4.0 * (double)n_circle/(double) NDARTS;
MPI_Reduce (&pi_current, &pi_sum, 1, MPI_DOUBLE, MPI_SUM, MASTER, MPI_COMM_WORLD);
if (proc_id == MASTER) {
pi_sum = pi_sum/n_procs;
error = fabs ((pi_sum -PI)/PI) *100;
end_time = MPI_Wtime();
printf("Known value of PI : %11.10f \n", PI);
printf("Estimated Value of PI : %11.10f\n", pi_sum);
printf("Error Percentage : %10.8f\n", error);
printf("Time : %10.8f\n\n", end_time - start_time);
}
MPI_Finalize();
return 0;
}