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Java Newton's Method HELP PLEASE

Discussion in 'Java' started by nickcanada, Apr 6, 2010.

  1. nickcanada

    nickcanada New Member

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    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!
    Code:
     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);
     do
     {
      rootEstimate = initialRootEstimate - (function/derivedFunction);
      absDifference = Math.abs(rootEstimate-initalRootEstimate);
      numLoops++;
      initialRootEstimate=rootEstimate;
      }
    
    Thank you!
     
  2. virxen

    virxen New Member

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    post the mathematics problem you are trying to solve.
     
  3. tech_aks

    tech_aks New Member

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    i m sending u a newton class..post ur sum...will let u know d solution...
    Code:
    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");
    	  }
         }
    
    }
     
    Last edited by a moderator: Apr 7, 2010
  4. nickcanada

    nickcanada New Member

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    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:
    Code:
    import java.io.*;
    
    public class Assignment1try2
    
    {
    
        public static void main(String[] args)
    
        {
            //Exports the data to an excel file
    
         PrintWriter outputFile = null;
           try
             {
               outputFile = new PrintWriter(new FileOutputStream("outputVelomobile.xls",false));
              }
                catch(FileNotFoundException e)
             {
               System.out.println("File error.  Program aborted.");
               System.exit(0);
              }
    
    
            //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;
    
            do
            {
    
            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];
            numLoops++;
    
             }
    
               while (absDifference >=1.0E-12);
    
                //Displays data on screen
                System.out.println();
                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);
                System.out.println();
    
                //Outputs results on screen
    
                outputFile.println();
                outputFile.println("The Power is:"    +   powerRider[index]);
                outputFile.println("The Root Estimate is:"    +   initialRootEstimate);
                outputFile.println("The number of cycles is:"    +   numLoops);
                outputFile.println();
    
    
            }
                outputFile.close();
        }
    
    }
    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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