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# Java Newbie needs help writing getting polynomial coordinates to graph.....using java

Posted on 2006-11-19
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I have written a program that askes a user for 4 coefficients,the number of points to graph,the starting point of x , and the interval that they're incremented by. Then the program finds f(x) from x for a given number of points. The last and final thing I am trying to get this program to do is to plot the points on a graph and connect them using straight lines. Most of the program is written so this shouldn't be too difficult except for me. The graph can assume that all coefficients passed to it are possitive, and only has an x value given to it between 0 and 5. Any help would be greatly appreciated. I will give you the code for the class and main method below.

import java.util.Scanner;
import java.text.DecimalFormat;

public class Poly
{
public static void main (String[] args)
{
double c4,c3,c2,c1,c0,x,interval,xvalue;
int ptnumber,counter;
String result;

DecimalFormat fmt = new DecimalFormat ("0.##");

Scanner scan = new Scanner (System.in);

System.out.print ("Enter the coefficient of x^4(0.0 if none:");
c4 = scan.nextDouble();

System.out.print ("Enter the coefficient of x^3(0.0 if none:");
c3 = scan.nextDouble();

System.out.print ("Enter the coefficient of x^2(0.0 if none:");
c2 = scan.nextDouble();

System.out.print ("Enter the coefficient of x^1(0.0 if none:");
c1 = scan.nextDouble();

System.out.print ("Enter the constant:");
c0 = scan.nextDouble();

System.out.print ("Enter the starting value of x:");
x = scan.nextDouble();

System.out.print ("Enter the number of points to be graphed(Integer):");
ptnumber = scan.nextInt();

System.out.print ("Enter the interval between points:");
interval = scan.nextDouble();

Polynomial pn = new Polynomial(c4, c3, c2, c1, c0);

System.out.println("f(x)="+pn);

System.out.println("x      | f(x)");
System.out.println("----------");
counter = 0;
while (counter < ptnumber)
{

System.out.println(x            +"      | "+fmt.format(pn.evaluate(x)));

x = (x + interval);
counter++;
}

}
}

POLY CLASS

import javax.swing.JPanel;
import java.awt.*;
import java.text.DecimalFormat;

import java.text.DecimalFormat;
public class Polynomial
{
double coeff4, coeff3, coeff2, coeff1, constant;
String sign4,sign3,sign2,sign1,sign0;
public Polynomial(double c4, double c3, double c2, double c1, double c0)
{
coeff4 = c4;
coeff3 = c3;
coeff2 = c2;
coeff1 = c1;
constant = c0;

}

public double evaluate(double x)
{

double xsq = x*x;
return (coeff4*xsq*xsq + coeff3*xsq*x + coeff2*xsq + coeff1*x + constant);

}

public String toString()

{
String result = "";

if (coeff4 != 0)
{
result += coeff4+"x^4";
}
if (coeff3 != 0)
{
if (coeff3 > 0)
result += "+";

result += coeff3+"x^3";
}
if (coeff2 != 0)
{
if (coeff2 > 0)
result += "+";

result += coeff2+"x^2";
}
if (coeff1 != 0)
{
if (coeff1 > 0)
result += "+";

result += coeff1+"x";
}
if(constant!=0)
{
if(constant>0)
result+="+";

result += constant;
}

return result;

}

public void draw(Graphics page, int xPixels, int yPixels)
{
final int NUM = 11;
final double INTERVAL = 0.5;
final double XSTART = 0.0;

final int XMARGIN = 70;
final int XUSABLEPIXELS = xPixels - 2*XMARGIN;
final int XINTERVALPIXELS = XUSABLEPIXELS/(NUM - 1);
final int YMARGIN =40;
final int YUSABLEPIXELS = yPixels - 2*YMARGIN;

// Label the graph
page.drawString("Graph of f(x) = " + toString(), XMARGIN + 20, YMARGIN);

// Draw the x axis and put in hash marks
page.drawLine(XMARGIN, yPixels - YMARGIN, xPixels - XMARGIN, yPixels - YMARGIN);
for ( int i = 0; i < NUM; i++ )
page.drawLine(XMARGIN + i * XINTERVALPIXELS, yPixels - YMARGIN, XMARGIN + i * XINTERVALPIXELS, yPixels - YMARGIN + 5);

DecimalFormat twoPlaces = new DecimalFormat("0.00");

// Label the x axis
for (int i = 0; i < NUM; i++)
{
page.drawString( twoPlaces.format(XSTART + i * INTERVAL), 3 * XMARGIN / 4 + i * XINTERVALPIXELS, yPixels - YMARGIN/2);
}

// Draw the y axis
page.drawLine(XMARGIN, YMARGIN, XMARGIN, yPixels - YMARGIN);

// Label the y axis and put in hash marks
final double YMIN = 0.0;
final double YINTERVAL = 100.0;
final int YINTERVALPIXELS = YUSABLEPIXELS / 10;

for (int i = 0; i < NUM; i++)
{
page.drawString(twoPlaces.format(YMIN + i * YINTERVAL), XMARGIN / 4, yPixels - i * YINTERVALPIXELS - YMARGIN);
page.drawLine(XMARGIN, yPixels - YMARGIN - i * YINTERVALPIXELS, XMARGIN - 5, yPixels - YMARGIN - i * YINTERVALPIXELS);
}

}
}

0
Question by:lusius188
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1 Comment

LVL 2

Accepted Solution

saintsairforce earned 500 total points
ID: 17980628
I just ansewered a simular question. This should help you out a lot

http://www.experts-exchange.com/Programming/Programming_Languages/Java/Q_22061802.html

Cheers,
Ricky
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