/*
c================================================================
c testing a random number generators
c rand  : standard C++ library
c the code
c 1. generates two arrays xr() and yr() with random numbers
c    between 0.0 and 1.0
c 2. calculates k-th momentum for both arrays (has to be 1.0/(k+1.0)
c 3. the near-neighbor correlation (has to be 0.25)
c
c written by Alex Godunov
c================================================================
*/
#include <iostream>
#include <fstream>
#include <iomanip>
#include <cstdlib>
#include <cmath>
#include <ctime>
using namespace std;

int main ()
{

int nmax = 100000;
double x[nmax], y[nmax];
double xm, ym, xth;
int    i, ix, iy, kmoment, kshift;

 ofstream file_1;
 ofstream file_2;
 file_1.open ("random03.dat");
 file_2.open ("random04.dat");

 file_1.precision(4);
 file_1.setf(ios::fixed | ios::showpoint);
 file_2.precision(4);
 file_2.setf(ios::fixed | ios::showpoint);
 cout.precision(4);
 cout.setf(ios::fixed | ios::showpoint); 

  xm = 0.0;
  ym = 0.0;

  kmoment = 3;
  kshift =  5;

// first random array: x(i)
  srand(time(NULL));
  for (i=0; i < nmax; i=i+1)
  {
      x[i] = 1.0*rand()/(RAND_MAX-1.0);
  }
// second random array: y(i)
  srand(time(NULL)-12345);
  for (i = 0; i < nmax; i=i+1)
  {
      y[i] = 1.0*rand()/(RAND_MAX-1.0);
  }  
// write x and y arrays together with k-th momentum      
  for (i = 0; i < nmax; i=i+1)
  {
      file_1 << setw(12) << x[i] << setw(12) << y[i] <<endl;
      xm=xm+(pow(x[i],kmoment))/nmax;
      ym=ym+(pow(y[i],kmoment))/nmax;     
  }
  xth = 1.0/(kmoment+1.0);
  cout << setw(5) << kmoment <<setw(12) << xm << setw(12) << ym << endl;

  xm = 0.0;
//c*** write correlation (same array)
//c and calculate the near-neighbor correlation (has to be close to 0.25)
  for(i = 0; i<nmax-kshift; i = i+1)
  {
      file_2 << setw(12) << x[i] << setw(12) << x[i+kshift] <<endl;
      xm = xm + x[i]*x[i+kshift]/nmax;
  }
  cout << setw(12) << xm << endl;

  return 0;
}