Calculate a Phi coefficient in Java

Question

I want to calculate a Phi coefficient in Java for a Confusion Matrix 2 x 2 where the code so far as below :

double str= (trueP + falseP) *(trueP + falseN) * (trueN + falseP) * (trueN + falseN);
               double output= Math.sqrt(str);
                if (output!= 0.0)
                return (trueP * trueN) / output;
            else return 0.0;

where the trueP=6930, trueN=6924, falseP=0, and falseN = 0, the output of this code is 3629.03401901938. I have calculated the Phi coefficient in excel it returns value 1 for the same values

What is the Wrong?

Any help will be highly appreciated

Answer 1

if every variable is double your code produces the desired output 1.0 :

just compile and run the following java class which assigns the values you want to be assigned to trueP, trueN, falseP and falseN:

class confusion {
    public static void main(String[] args) {
    double trueP=6930;
    double trueN=6924;
    double falseP=0;
    double falseN=0;
    double str= (trueP + falseP) *(trueP + falseN) * (trueN + falseP) * (trueN + falseN);
               double output= Math.sqrt(str);
                if (output!= 0.0) {
                    double output2 =(trueP * trueN) / output;
                    System.out.println(output2);
            }
                else  {
                System.out.println(output); // Display the string.
            }
    }
}

the reason is that double can hold a max value big enough for your case:

static double   MAX_VALUE
A constant holding the largest positive finite value of type double, (2-2-52)·21023.

as you can see here : http://docs.oracle.com/javase/7/docs/api/java/lang/Double.html