PolyGrapher - Graphing Polynomials

Requirements for the graph

• must be drawn with x increasing to the right and y increasing upwards (10 pts.)
• must ask for user input for the coefficients of an n-degree polynomial (10 pts.)
• must ask for user input for the range  [a, b] over which the polynomial is to be evaluated  (10 pts.)
• must display grid lines every 10 pixels in both the X and Y directions in a light color on an 800 by 600 image (10 pts.)
• must plot the polynomial in the figure at nearly 800 points  (15 pts.)
• must be scaled so as to occupy nearly all the space available with all features of the graph displayed over the plot range (10 pts.)
• must print to the console the polynomial's toString, range [a, b] min, max, scale factor (10 pts.)
• must plot the polynomial's derivative function in the same figure using the original polynomial's scale factor, range, nPoints and minimum value in a different color  (15 pts.)
• must print to the console the derivative's toString (10 pts.)
• may display abscissa and ordinate axes  about the origin in black whenever contained in the function's plot over the given range (5 bonus pts.)
• may have a 20 pixel border on three sides for text / aesthetics (2 bonus pts.)

Program Design

The PolyGrapher class

• public void plot(): When invoked, this method
  • Clears all existing graphs off the screen
  • prompts the user for the values of the coefficients for a polynomial
  • instantiates a polynomial with the data obtained in the previous step
  • prompts the user for the range [a, b] over which the polynomial is to be evaluated
  • invokes getGraphData() with the polynomial, range and number of points to plot and returns a data array with yMin, yMax and sf.
  • invokes graph() with the polynomial, data array with yMin, yMax and sf, and a color not used for the grid lines or axes.
• public double[] getGraphData(Polynomial p, double a, double b, int nPoints) When invoked, this method determines the values nPoints, yMin, yMax, and sf
  • Evaluates the polynomial at the appropriate values for x compute maximum and minimum values of the function on [a, b].
  • Computes the scaling factor sf.  sf = graphHeight / ( max - min ).
• public void plotAndDifferentiate(): When invoked, this method
  • invokes plot()
  • invokes the current polynomial's differentiate method to get a new polynomial, the derivative of the current polynomial
  • invokes graph() with the new polynomial, same data, and a new color.
• private double[] graph(Polynomial p, double[] data, Color c): When invoked, this method displays the line graph of the polynomial in an 800x600 image plotted from a through b on nPoints using the color c.
  • Evaluates the polynomial at the appropriate values for x
  • Displays the line graph of the polynomial in an 800x600 image.
  • Returns the scale factor and minimum value of the plot.
• Other methods as desired to make your code more readable/useable.

The Polynomial class

• A constructor: public Polynomial(double [] coefficients)
• public double evaluate(double x) - returns the value of the polynomial at the specified value for x.
• public Polynomial differentiate() - returns a new polynomial, the derivative of this polynomial.
• public String toString() - returns a string representation of this polynomial

Sample output:

2.0x^3 + 1.5x^2
a = -10.0, b = 10.0, n = 760, dx = 0.02631578947368421, min = -1850.0, max = 2150.0, sf = 0.14975.

6.0x^2 + 3.0x
derivative's a = -10.0, b = 10.0, n = 760, dx = 0.02631578947368421, derivMin = -0.3739612188365653, sf = 0.14975.