Java
import java.util.Random;
import java.math.*;
public class MonteCarlo {
static final int iter = 100000;
static final int max_rep = 5000;
/*I aware of the fact that such public variable declarations are bad for OO design.But for the sake of performance…*/
public static int in_region[];
public static Random r;
public static void EstimatePI(int rep) {
double x, y;
int i, j;
double mean = 0, var = 0, hl;
for (j = 0; j < rep; j++) {
in_region[j]=0;
for (i = 0; i < iter; i++) {
x = 2 * r.nextDouble() - 1;
y = 2 * r.nextDouble() - 1;
if (x * x + y * y <= 1) {
in_region[j]++;
}
}
mean += in_region[j] * 1.0 / rep;
}
if (rep > 1) {
for (i = 0; i < rep; i++) {
var += (in_region[i] - mean) * (in_region[i] - mean) / (rep - 1);
}
}
mean = 4 * mean / iter;
hl = 7.84 * Math.sqrt(var/rep) / iter;
System.out.println("PI estimation is " + mean + " with half-length " + hl);
}
public static void main(String[] args) {
MonteCarlo mc = new MonteCarlo();
mc.r=new Random();
mc.in_region = new int[mc.max_rep];
long start;
for (int r = 1; r <= mc.max_rep; r *= 4) {
start = System.currentTimeMillis();
MonteCarlo.EstimatePI(r);
System.out.println("Response time is " + (System.currentTimeMillis() - start)/1000.0 + " sec.");
System.out.println();
}
}
}
C
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <math.h>
#define ITER 100000
#define MAX_REP 5000
int in_region[MAX_REP];
void EstimatePI(int rep){
int i,j;
double mean=0,var=0,hl,x,y;
srand(time(NULL));
for (j = 0; j < rep; j++) {
in_region[j]=0;
for (i = 0; i < ITER; i++) {
x = 2.0 * rand()/RAND_MAX - 1;
y = 2.0 * rand()/RAND_MAX - 1;
if (x * x + y * y <= 1) {
in_region[j]++;
}
}
mean += in_region[j] * 1.0 / rep;
}
if (rep > 1) {
for (i = 0; i < rep; i++) {
var += (in_region[i] - mean) * (in_region[i] - mean) / (rep - 1);
}
}
mean = 4 * mean / ITER;
hl = 7.84 * sqrt(var/rep) / ITER;
printf("PI estimation is %7.5lf with half-length %7.5lf\n",mean,hl);
}
int main(int argc, char* argv[]){
int r;
unsigned int start;
srand(time(NULL));
for (r = 1; r <= MAX_REP; r *= 4) {
start = time(NULL);
EstimatePI(r);
printf("Response time is %d sec.\n\n",time(NULL) - start);
}
return 0;
}