/***********************************************************************
 *
 * File: histo.c (16-Jun-2001)
 *               (20-Jun-2005)
 *
 * Mittelwert, Varianz und Wahrscheinlichkeitsdichte der
 * gleichverteilten Zufallsvariablen x auf dem Intervall [0,1]
 *
 * nbins.........Anzahl der Histogrammkanaele
 * n.............Stichprobenumfang
 * "histo.dat"...Ausgabefile fuer Histogramm
 *
 **********************************************************************/

#include <stdio.h>
#include <stdlib.h>

/**********************************************************************/

int main () {

/**********************************************************************/

  FILE *fp;
  int i,k,n,nbins;
  int *ihist;
  const double a=0.0,b=1.0;
  double ax,axx,x;
  
  printf(" nbins=");
  scanf("%d",&nbins);
  printf("     n=");
  scanf("%d",&n);

  ihist=(int*)malloc(nbins*sizeof(int));

  ax=0.0;
  axx=0.0;
  for(k=0;k<=nbins-1;k=k+1) {
    ihist[k]=0;
  }
  
  for(i=1;i<=n;i=i+1) {
    x=a+(b-a)*drand48();
    ax=ax+x;
    axx=axx+x*x;
    k=(x-a)/(b-a)*nbins;
    if(k>=nbins-1) {
      k=nbins-1;
    }
    ihist[k]=ihist[k]+1;
  }

  printf("    <x>=%14.7e\n",ax/n);
  printf(" Var(x)=%14.7e\n",(axx-ax*ax/n)/(n-1));

  fp=fopen("histo.dat","w");
  
  for(k=0;k<=nbins-1;k=k+1) {
    x=a+(k+0.5)*(b-a)/nbins;
    fprintf(fp," %14.7e %14.7e\n",x,((double)ihist[k])*nbins/(n*(b-a)));
  }

  fclose(fp);
  
  return 0;
  
}

/**********************************************************************/