JavaAlgorithms/Maths/PiNilakantha.java

package Maths;

public class PiNilakantha {

  // Calculates Pi using Nilakantha's infinite series
  // Method 2 in the following link explains the algorithm
  // https://en.scratch-wiki.info/wiki/Calculating_Pi

  public static void main(String[] args) {
    assert calculatePi(0) == 3.0;
    assert calculatePi(10) > 3.0;
    assert calculatePi(100) < 4.0;

    System.out.println(calculatePi(500));
  }

  /**
   * @param iterations number of times the infinite series gets repeated Pi get more accurate the
   *     higher the value of iterations is Values from 0 up to 500 are allowed since double
   *     precision is not sufficient for more than about 500 repetitions of this algorithm
   * @return the pi value of the calculation with a precision of x iteration
   */
  public static double calculatePi(int iterations) {
    if (iterations < 0 || iterations > 500) {
      throw new IllegalArgumentException("Please input Integer Number between 0 and 500");
    }

    double pi = 3;
    int divCounter = 2;

    for (int i = 0; i < iterations; i++) {

      if (i % 2 == 0) pi = pi + 4.0 / (divCounter * (divCounter + 1) * (divCounter + 2));
      else pi = pi - 4.0 / (divCounter * (divCounter + 1) * (divCounter + 2));

      divCounter += 2;
    }
    return pi;
  }
}