Question

I had to write this for a class project. I don’t get any errors when compiling, but the program won’t run when I attempt to execute it.

We have to write a program myRandomWalkers.java that takes two command-line arguments N and T. In each of T independent experiments, simulate a random walk of N steps and compute the squared distance. Output the mean squared distance (the average of the T squared distances).

I wrote the following:

public class myRandomWalkers {

    public static void main(String[] args) {

        int n= Integer.parseInt(args[0]);
        int t= Integer.parseInt(args[1]);
        int x= 0; // starting x position
        int y= 0; // starting y position
        int sum = 0; // for calculating mean square distance
        double r;

        int count = 0;
        while (count <= t)
        {
            for (int i=0; i<n; i++) {

                r= Math.random();
                if (r<=0.25) x++;
                else if(r<=0.50) x--;
                else if(r<=0.75) y++;
                else if(r<=1.0) y--;        

                int z = ((x*x) + (y*y));
                sum +=z;
            }
        }

        int average = (sum/t);
        System.out.println ("mean squared distance = " + average);
    }        
}

Thanks in advance!

Answer 1

The output will depend on the arguments you pass to your program. However:

• if count > t the while loop will not be executed
• if count <= t the while loop will never end because you don’t increment count – you probably need to add a count++; somewhere in your while loop.