Formula with Random Number Generator

Question

Having a bit of an issue here. Wondering why I am getting "Infinity" for my result for my arrivalInterval method. (tmp is defined in a previous class, I will paste both classes) The first class, RandomNum, works just fine.

import java.util.Random;

public class RandomNum {

        static double x = 0.1;
        static double y = 0.2;
        static double z  = 0.3; 
        static double lamda;                                  
        static double tmp;
        static double count1, count2, count3;
        static double average;          
        static Random randomNumbGen = new Random();

        // 3 methods for testing x, y, and z
        public static double ExpInterval(double lamda)

        {
        tmp=randomNumbGen.nextDouble();            
        return (-(1/lamda) * Math.log(tmp));
        }

        public static void main(String[] args) {
                   // TODO Auto-generated method stub
                    // loop that runs then methods then adds them to the count (for an an average later)     and prints out the results

for (int i=1; i<1001; i++)
count1+=ExpInterval(x);
System.out.println(ExpInterval(x));
count2+=ExpInterval(y);
System.out.println("                         " + ExpInterval(y));
count3+=ExpInterval(z);
System.out.println("                                                       " + ExpInterval(z));
}



//calculates average then prints it out
average = count1/1000;
System.out.println("The Average of the first variable is" + average +"  " + "1/lamba is " + 1/x);
average = count2/1000;
System.out.println("The average of the second variable is " + average + "   " + "1/lamba is " + 1/y);
average = count3/1000;
System.out.println("The average of the third variable is " +  average + "   " +  "1/lamba is " + 1/z);
}}

now for the class I am having the issue with. If the random number picks 1, then divide .1/tmp(random number generated in first class), if 2, then .2/tmp, and if 3, then .3/tmp

    import java.util.*;
    public class RandomProcess extends RandomNum 
    {
    Set<Integer> set = new HashSet<Integer>();
    Random random = new Random();
    public double findArrivalInterval()
    {
    double arrivalInterval = 0.0;
    set.add(1);
    set.add(2);
    set.add(3);
    Integer result = (Integer) set.toArray()[random.nextInt(set.size())]; //only 1, 2, or 3 to be picked

    if (result == 1)
    {
    arrivalInterval = .1/tmp;
    System.out.println(arrivalInterval);
    return arrivalInterval;
    }
    if (result == 2)
    {
    arrivalInterval = .2/tmp;
    System.out.println(arrivalInterval);
    return arrivalInterval;

    }
    if (result == 3)
    {
    arrivalInterval = .3/tmp;
    System.out.println(arrivalInterval);
    return arrivalInterval;
    }
    System.out.print(arrivalInterval);
    return arrivalInterval;
    }
        public static void main(String[] args)
        {
        RandomProcess testProcess = new RandomProcess();
        testProcess.findArrivalInterval();
        }
    }

Answer 1

It seems tmp == 0f; Java floating-point division-by-zero produces either POSITIVE_INFINITY or NEGATIVE_INFINITY depending on the sign.

The reason tmp is 0f is because you never assign to it, so it keeps its default initialization value, which is 0f. Note that you never call ExpInterval, so indeed tmp is never modified in the code you posted.

Answer 2

You never set tmp in the second class because you never call ExpInterval, just findArrivalInterval.

Also, you can write int result = (Math.random()*3)+1 instead of all that stuff with set. And replace all those if statements with

arrivalInterval = 0.1*result/tmp
System.out.println(arrivalInterval);
return arrivalInterval;