Java - Ramanujan Series for pi

Question

For one of my programs in my Computer Science class I have to calculate the value of pi using the following formula, I'm having trouble with the math equation in java.

Here's the math formula: Formula for 1/pi

the formulas I used were:

for (int i = 0; i < k; i++) 
{
   term = ((calculate(4*i)*(1103+(26390*i)))/(Math.pow(calculate(i), 4))*Math.pow(396, (4*i)));
   sum += term;
}
sum *= ((2*Math.sqrt(2))/9801);
sum = Math.pow(sum, -1);

The for loop should calculate the sigma sign and everything to the right of it. The next part should multiply that number by 2 square roots of 2 divided by 9801 and the final part should take that number to the -1st power, since the equation finds 1/pi this should reciprocate the fraction.

the calculate method just finds the factorial of a number.

When I run the program, the final answer is exactly pi at 1, 2.1355575437204093E-13 at 2, and it keeps printing wrong numbers. Any idea why this could be giving the wrong answer?

Thanks, any help is appreciated!

Answer 1

you had your brackets wrong for your denominator:

term = (double)(calculate(4*i)*(1103+(26390*i)))/((Math.pow(calculate(i), 4))*Math.pow(396, (4*i)));

Try using doubles for your calculations. And with a value of k = 30, the result is 3.141592653589793

And determining the value of PI is like applying stochastics to find a deterministic value, using large iterations gives a better precision