Newton's Method

Code:


import java.util.Scanner;

/**
 *
 * @author ThienDinh
 */
public class Homework {

    /**
    * @param args the command line arguments
    */
    public static void main(String[] args)
    {
        // TODO code application logic here
        Scanner in = new Scanner(System.in);
        /*
        * Newton's Method
        * Round off to 8th decimal, each calculation
        * Function using is f(x) = 3x^3 - 9x + 2 and its derivative f'(x) = 9x^2 - 9
        * First picked x = 0 -> fx = 2 -> dfx = -9 (Calculated by hand)
        */
        double x = 0;
        double fx = 2;
        double dfx = -9; // dfx : f'
        System.out.print("n = ");
        int n = in.nextInt();
        System.out.println("--------------------------------------------------------------------");
        System.out.printf("n = 1\t");
        System.out.printf("x: %.8f\t", x);
        System.out.printf("f(x): %.8f\t", fx);
        System.out.printf("f'(x): %.8f\n", dfx);
        for (int i = 2; i <= n; i++)
        {
            String temp = "";
            System.out.println("--------------------------------------------------------------------");
            System.out.printf("n = %d\t", i);
           
            temp = "" + String.format("%.8f", x - (fx / dfx)); // Xn = X - (Fx / F'x)
            x = Double.parseDouble(temp);
            System.out.printf("x: %.8f\t", x);
           
            temp = "" + String.format("%.8f", 3 * Math.pow(x, 3) - 9 * x + 2); // Function
            fx = Double.parseDouble(temp);           
            System.out.printf("f(x): %.8f\t", fx);
           
            temp = "" + String.format("%.8f", 9 * Math.pow(x, 2) - 9); // Derivative funtion
            dfx = Double.parseDouble(temp);
            System.out.printf("f'(x): %.8f\n", dfx);
        }
    }
}


n = 5
--------------------------------------------------------------------
n = 1 x: 0.00000000 f(x): 2.00000000 f'(x): -9.00000000
--------------------------------------------------------------------
n = 2 x: 0.22222222 f(x): 0.03292183 f'(x): -8.55555556
--------------------------------------------------------------------
n = 3 x: 0.22607023 f(x): 0.00002975 f'(x): -8.54003026
--------------------------------------------------------------------
n = 4 x: 0.22607371 f(x): 0.00000003 f'(x): -8.54001610
--------------------------------------------------------------------
n = 5 x: 0.22607371 f(x): 0.00000003 f'(x): -8.54001610
BUILD SUCCESSFUL (total time: 6 seconds)