xexpdev.c

Numerical Recipes in C的源代码

/* Driver for routine expdev */

#include <stdio.h>
#include <math.h>
#define NRANSI
#include "nr.h"

#define NPTS 10000
#define EE 2.718281828

int main(void)
{
	long idum=(1);
	int i,j,total=0,x[21];
	float expect,xx,y,trig[21];

	for (i=0;i<=20;i++) {
		trig[i]=i/20.0;
		x[i]=0;
	}
	for (i=1;i<=NPTS;i++) {
		y=expdev(&idum);
		for (j=1;j<=20;j++)
			if ((y < trig[j]) && (y > trig[j-1])) ++x[j];
	}
	for (i=1;i<=20;i++) total += x[i];
	printf("\nexponential distribution with %7d points\n",NPTS);
	printf("    interval      observed     expected\n\n");
	for (i=1;i<=20;i++) {
		xx=(float) x[i]/total;
		expect=exp(-(trig[i-1]+trig[i])/2.0);
		expect *= (0.05*EE/(EE-1));
		printf("%6.2f %6.2f %12.6f %12.6f \n",
			trig[i-1],trig[i],xx,expect);
	}
	return 0;
}
#undef NRANSI