edu.rit.numeric

Class Cubic

java.lang.Object

edu.rit.numeric.Cubic

public class Cubic
extends java.lang.Object

Class Cubic solves for the real roots of a cubic equation with real coefficients. The cubic equation is of the form

ax³ + bx² + cx + d = 0

To solve a cubic equation, construct an instance of class Cubic; call the Cubic object's solve() method, passing in the coefficients a, b, c, and d; and obtain the roots from the Cubic object's fields. The number of (real) roots, either 1 or 3, is stored in field nRoots. If there is one root, it is stored in field x1, and fields x2 and x3 are set to NaN. If there are three roots, they are stored in fields x1, x2, and x3 in descending order.

The same Cubic object may be used to solve several cubic equations. Each time the solve() method is called, the solution is stored in the Cubic object's fields.

The formulas for the roots of a cubic equation come from:

E. Weisstein. "Cubic formula." From MathWorld--A Wolfram Web Resource. http://mathworld.wolfram.com/CubicFormula.html

Field Summary

Fields

Modifier and Type	Field and Description
int	nRoots The number of real roots.
double	x1 The first real root.
double	x2 The second real root.
double	x3 The third real root.

Constructor Summary

Constructors

Constructor and Description
Cubic() Construct a new Cubic object.

Method Summary

Modifier and Type	Method and Description
static void	main(java.lang.String[] args) Unit test main program.
void	solve(double a, double b, double c, double d) Solve the cubic equation with the given coefficients.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

nRoots

public int nRoots

The number of real roots.

x1

public double x1

The first real root.

x2

public double x2

The second real root.

x3

public double x3

The third real root.

Constructor Detail

Cubic

public Cubic()

Construct a new Cubic object.

Method Detail

solve

public void solve(double a,
                  double b,
                  double c,
                  double d)

Solve the cubic equation with the given coefficients. The results are stored in this Cubic object's fields.

Parameters:

a - Coefficient of x³.

b - Coefficient of x².

c - Coefficient of x.

d - Constant coefficient.

Throws:

DomainException - (unchecked exception) Thrown if a is 0; in other words, the coefficients do not represent a cubic equation.

main

public static void main(java.lang.String[] args)
                 throws java.lang.Exception

Unit test main program.

Usage: java edu.rit.numeric.Cubic a b c d

Throws:

java.lang.Exception