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nickcanada 7Apr2010 03:08

Java Newton's Method HELP PLEASE
Hey I'm a total beginner to Java and I could really use some help with this program please!
This is part of the code I wrote. I put a do-while loop but this only takes care of the rootEstimate value, the powerRider value is also changing. Basically I need to end up with my answer for the root Estimate then after I got the answer with the first power, switch to the second power. The powerRider variable is declared as an array. I was thinking of possibly having a loop with an increment encasing the do-while loop which would increase whenever the while part is not met, but I'm not 100% sure how to approach this and some help would be appreciated!

function = -n*powerRider + 0.5*(rho*cD*area*(Math.pow(initialRootEstimate,3))) + (cR*m*g*initialRootEstimate);
 derivedFunction = (3/2)*(rho*cD*area*(Math.pow(initialRootEstimate,2))) + (cR*m*g);
  rootEstimate = initialRootEstimate - (function/derivedFunction);
  absDifference = Math.abs(rootEstimate-initalRootEstimate);

Thank you!

virxen 7Apr2010 04:52

Re: Java Newton's Method HELP PLEASE
post the mathematics problem you are trying to solve.

tech_aks 7Apr2010 12:01

Re: Java Newton's Method HELP PLEASE
i m sending u a newton class..post ur sum...will let u know d solution...

class Newton  {

    static double f(double x) {
        return Math.sin(x);

    static double fprime(double x) {
        return Math.cos(x);

    public static void main(String argv[]) {

          double tolerance = .000000001; // Our approximation of zero
          int max_count = 200; // Maximum number of Newton's method iterations

/* x is our current guess. If no command line guess is given,
  we take 0 as our starting point. */

          double x = 0;

          if(argv.length==1) {
            x= Double.valueOf(argv[0]).doubleValue();

        for( int count=1;
                  (Math.abs(f(x)) > tolerance) && ( count < max_count);
                count ++)  {
            x= x - f(x)/fprime(x);
            System.out.println("Step: "+count+" x:"+x+" Value:"+f(x));

          if( Math.abs(f(x)) <= tolerance) {
          System.out.println("Zero found at x="+x);
          else {
          System.out.println("Failed to find a zero");


nickcanada 7Apr2010 21:49

Re: Java Newton's Method HELP PLEASE
Hey sorry I've been working on it so haven't had a chance to check back. Thanks for the help! So far I've written this:

import java.io.*;

public class Assignment1try2


    public static void main(String[] args)

        //Exports the data to an excel file

    PrintWriter outputFile = null;
          outputFile = new PrintWriter(new FileOutputStream("outputVelomobile.xls",false));
            catch(FileNotFoundException e)
          System.out.println("File error.  Program aborted.");

        //Variable declarations for the Quest Velomobile

    double n = 0.92;
    double rho = 1.20;
    double cR = 0.004;
    double m = 32+80;
    double g = 9.81;
    double cD = 0.24;
    double area = 0.46;
    double valueOne = rho*cD*area;
    double valueTwo = cR*m*g;
    double initialRootEstimate = 1;
    double function, absDifference;
    double[] rootEstimate = new double[8];
    int numLoops = 0;
    int[] powerRider = {25,50,75,100,150,200,300,400};

        //Start loop
    for (int index=0;index<powerRider.length;index++)


        numLoops = 0;


        function = -n*powerRider[index] + 0.5*(valueOne*(Math.pow(initialRootEstimate,3))) + (valueTwo*initialRootEstimate);

        rootEstimate[index] = initialRootEstimate - (function/((3/2)*(valueOne*(Math.pow(initialRootEstimate,2))) + (valueTwo)));

        absDifference = Math.abs(rootEstimate[index] - initialRootEstimate);

        initialRootEstimate = rootEstimate[index];


          while (absDifference >=1.0E-12);

            //Displays data on screen
            System.out.println("The Power is:"    +  powerRider[index]);
            System.out.println("The Root Estimate is:"    +  initialRootEstimate);
            System.out.println("The number of cycles is:"    +  numLoops);

            //Outputs results on screen

            outputFile.println("The Power is:"    +  powerRider[index]);
            outputFile.println("The Root Estimate is:"    +  initialRootEstimate);
            outputFile.println("The number of cycles is:"    +  numLoops);



It works but the only problem is that we end up with a lot of iterations. Is there any way we can reduce the amount of iterations?

thanks again

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