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Thread: NewtonRaphson java code help
 06192013, 03:50 AM #1Member
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NewtonRaphson java code help
import java.util.Scanner;
import javax.swing.JOptionPane;
import java.text.DecimalFormat;
public class NewtonRaphsonMethod
{
public static void main(String[] args)
{
Scanner scan = new Scanner (System.in);
DecimalFormat fmt = new DecimalFormat ("0.###############");
String degreeCount, funcCoefficient, coefficentCount, userGuess, notEnough;
int degree, coefficient, a = 1, b = 0;
double guess, equation = 0, again = 1, x, fX, fPrimeX, rTotal, x1;
double[] xn = new double[1000];
double[] xn1 = new double[1000];
do
{
degreeCount = JOptionPane.showInputDialog("Please enter the degree of your polynomial below");
degree = Integer.parseInt(degreeCount);
funcCoefficient = "Please enter the " + (degree + 1) + " coefficents from highest degree to lowest degree in order";
JOptionPane.showMessageDialog(null, funcCoefficient);
int[] coefficientIndex = new int[degree + 1];
for (int count = 0; count < coefficientIndex.length; count++)
{
coefficentCount = JOptionPane.showInputDialog("Enter the coefficient below:");
coefficient = Integer.parseInt(coefficentCount);
coefficientIndex[count] = coefficient;
}
userGuess = JOptionPane.showInputDialog("Enter your initial guess (within a 1 decimal point threshold of the answer): ");
guess = Double.parseDouble(userGuess);
xn[0] = guess;
if (coefficientIndex.length < (degree + 1))
{
notEnough = "The number of coefficients you entered does not match the degree of the polynomial you gave.";
JOptionPane.showMessageDialog(null, notEnough);
}
int degree2 = degree;
System.out.println("Your polynomial function is f(x) = ");
for (int polynomial = 0; polynomial < (degree+1); polynomial++)
{
if (polynomial < degree)
{
System.out.print(coefficientIndex[polynomial] + "x^" + degree2 + " + ");
}
else
{
System.out.print(coefficientIndex[polynomial] + "x^" + degree2);
}
degree2;
}
int degree3 = degree;
double addTot = 0;
for (int fX1 = 0; fX1 < (degree+1); fX1++)
{
fX = coefficientIndex[fX1] * Math.pow(guess, degree3);
degree3;
addTot = addTot + fX;
}
int degree4 = degree;
double addTot2 = 0;
for (int fPrimeX1 = 0; fPrimeX1 < (degree+1); fPrimeX1++)
{
fPrimeX = (degree4 * coefficientIndex[fPrimeX1]) * Math.pow(guess, (degree4  1));
degree4;
addTot2 = addTot2 + fPrimeX;
}
rTotal = addTot/addTot2;
x1 = guess  rTotal;
while (guess != x1)
{
guess = x1;
xn[a] = guess;
a++;
degree3 = degree;
addTot = 0;
for (int fX1 = 0; fX1 < (degree+1); fX1++)
{
fX = coefficientIndex[fX1] * Math.pow(guess, degree3);
degree3;
addTot = addTot + fX;
}
degree4 = degree;
addTot2 = 0;
for (int fPrimeX1 = 0; fPrimeX1 < (degree+1); fPrimeX1++)
{
fPrimeX = (degree4 * coefficientIndex[fPrimeX1]) * Math.pow(guess, (degree4  1));
degree4;
addTot2 = addTot2 + fPrimeX;
}
rTotal = addTot/addTot2;
x1 = guess  rTotal;
xn1[b] = x1;
b++;
}
xn1[b++] = x1;
System.out.println("\r");
System.out.println("xn values");
for (int i = 0; i < a; i++)
{
System.out.println(fmt.format(xn[i]));
}
System.out.println("\n\n");
System.out.println("xn+1 values");
for (int n = 0; n < b; n++)
{
System.out.println(fmt.format(xn1[n]));
}
}
while (again == JOptionPane.YES_OPTION);
System.out.println(" ");
System.out.println("The root of the polynomial is: " + xn1[b  1]);
}
}
This is a code implementing the Newton Raphson method (for polynomials) for a school project. This method helps you find the zero(es) of a function and in the code you need to know the zero beforehand as the zero that you enter as an initial guess in this program is supposed to be in a 0.1 decimal point threshold. The polynomial for which our teacher checked us where the program did not fully work is: 4x^4  2x^3 92x^2 + x + 45. The program worked when 4.5, one zero of the function was entered, but the program did not work when 0.7 was entered for the function although it was within a 0.1 threshold of the actual zero (0.701....). I know the error is on line 95 which I palpably pointed out above since this is the error I keep getting when I enter 0.7: Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 1000 at NewtonRaphsonMethod.main(NewtonRaphsonMethod.java: 95). Please no hints or sarcastic replies, I just need a full answer to how to solve this, I understand that the problem is related to the array but I still can't wrap my head around why 4.5 would work but 0.7 did not even though I entered the correct zero near 0.7 for the function and it still didn't work.
 06192013, 07:05 AM #2
Re: NewtonRaphson java code help
If you're forever cleaning cobwebs, it's time to get rid of the spiders.
 06192013, 02:06 PM #3
 Join Date
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 Location
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Re: NewtonRaphson java code help
4.5 isn't a root of that polynomial (f(4.5) == 364.5); My Jenkins Traub implementation gives the following roots:
5.0107051936
4.4879589227
0.7187625169
0.696016246
Try a first approximation to the left of the smallest root and to the right of the largest root.
kind regards,
Joscenosillicaphobia: the fear for an empty beer glass
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