/***************************************************************************
This program creates a randomized array of initial velocities of either -1
or 1, with N/2 of each.  I choose N/2 sites randomly. Sites in this list 
are given velocity +1, the others -1.

Original version by Deva O'Neil.  Modified by Peter Young.
**************************************************************************/
#include <time.h>
#include <math.h>
#include <stdlib.h>
#include <stdio.h>

void random_vs (int N, double v[])
{
    int k, num;
    double sum;
    int taken[N] ;  	// shows whether a given number is already taken 

    srand(time(NULL));  // Seed the random number generator

    for(k=0; k<N; k++) 
    {
	v[k] = -1.0;    // Initially set all the velocities to be -1 
	taken[k] = 0;   // Indicates that all sites are initially not taken 
    }

    for(k=0; k<N/2; k++) // Main loop gives k/2 random sites with +1 velocities
    {
       while(1)          // Continue until get a number that isn't taken 
       {
	    num = rand()%N;
	    if (taken[num] == 0) // We have a number that isn't taken 
	    {
		taken[num] = 1;  // num is now taken 
		break;   	 // Exit from the loop 
	    }
       } 
       v[num] = 1.0; 	 // Set velocity of site "num" to be +1 
    }		 	 // End of main loop 
    
    			 // Omit the rest from here once the routine
			 // works
    sum = 0;		 // Test if it worked. Print out v[k]'s and the sum.
    for(k=0; k<N; k++)
    {
	printf("v[%2d]= %10.4f\n",k,v[k]); // Print out the velocities 
	sum += v[k];
    }
    printf("sum  = %10.4f\n", sum); // Print out the sum; should be zero.
}