Calculate pi using Leibniz series

Question

I'm new to java and i'm trying to make a program that calculates pi using the Leibniz series with 100000 iterations. I need to define a method and call it. When I run my program I don't get a result. Could someone please tell me what I'm doing wrong and help me get back on track?

public class pi
{
    public static void main(String[] args)
    {
         double pi = computePi(100000); 
    }
    public static double computePi(int count) 
    {
        double pi = 0;
        count = 100000;
       
        for(int i =0; i<count; i++)
        {
            pi = Math.pow(-1,i)/(2*i+1);

        }
        return pi;
    }
}

Answer 1

If you want to print it to the console, try:

public static void main(String[] args)
{
     System.out.println("pi = " + calculatePi(100000)); 
}

I can't say much for the precision, though.

Answer 2

There are a couple things wrong with your code. First the function call in main does not match the name of the computePi function. Secondly, in the for loop you re-assign the value of the pi variable during each iteration. What you need to do is take the sum of all iterations. Therefore, you need to preserve the previous value of pi and add the current quotient to it. Finally, the Leibnez summation formula returns pi/4, not pi. Therefore you should change the return value to pi * 4.

public static void main(String[] args)
{
     double pi = computePi(100000); 
     System.out.println(pi);
}

public static double computePi(int count) 
{
    double pi = 0;

    for(int i = 0; i < count; i++)
    {
        pi += Math.pow(-1,i)/(2*i+1);
    }
    return pi * 4;
}

A final note: when you pass a parameter, you do not necessarily need to restore it into a variable. Just use the parameter value.

Answer 3

There are a number of issues in your code. For one, you don't print the result of your function. For another, your implementation appears to be off. I think you wanted,

public static void main(String[] args) {
    double pi = computePi(100000);
    System.out.println(pi);
}

public static double computePi(int count) {
    double pi = 1;

    for (int i = 3; i < count; i += 4) {
        pi = pi - (1 / (double) i) + (1 / (double) (i + 2));
    }
    return pi * 4;
}

Output is

3.141612653189785

Or you could use the built-in Math.PI constant,

System.out.println(Math.PI);

Output is

3.141592653589793