uk.ac.starlink.dpac.math

Class PolynomialFunction

java.lang.Object

uk.ac.starlink.dpac.math.PolynomialFunction

public class PolynomialFunction
extends Object

Immutable representation of a real polynomial function with real coefficients.

Horner's Method is used to evaluate the function.

Constructor Summary

Constructors

Constructor and Description
PolynomialFunction(double[] c) Construct a polynomial with the given coefficients.

Method Summary

Modifier and Type	Method and Description
int	degree() Returns the degree of the polynomial.
boolean	equals(Object obj)
protected static double	evaluate(double[] coefficients, double argument) Uses Horner's Method to evaluate the polynomial with the given coefficients at the argument.
double[]	getCoefficients() Returns a copy of the coefficients array.
int	hashCode()
String	toString() Returns a string representation of the polynomial.
double	value(double x) Compute the value of the function for the given argument.

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

PolynomialFunction

public PolynomialFunction(double[] c)

Construct a polynomial with the given coefficients. The first element of the coefficients array is the constant term. Higher degree coefficients follow in sequence. The degree of the resulting polynomial is the index of the last non-null element of the array, or 0 if all elements are null.

The constructor makes a copy of the input array and assigns the copy to the coefficients property.

Parameters:

c - Polynomial coefficients.

Method Detail

value

public double value(double x)

Compute the value of the function for the given argument.

The value returned is

coefficients[n] * x^n + ... + coefficients[1] * x + coefficients[0]

Parameters:

x - Argument for which the function value should be computed.

Returns:

the value of the polynomial at the given point.

degree

public int degree()

Returns the degree of the polynomial.

Returns:

the degree of the polynomial.

getCoefficients

public double[] getCoefficients()

Returns a copy of the coefficients array.

Changes made to the returned copy will not affect the coefficients of the polynomial.

Returns:

a fresh copy of the coefficients array.

evaluate

protected static double evaluate(double[] coefficients,
                                 double argument)

Uses Horner's Method to evaluate the polynomial with the given coefficients at the argument.

Parameters:

coefficients - Coefficients of the polynomial to evaluate.

argument - Input value.

Returns:

the value of the polynomial.

toString

public String toString()

Returns a string representation of the polynomial.

The representation is user oriented. Terms are displayed lowest degrees first. The multiplications signs, coefficients equals to one and null terms are not displayed (except if the polynomial is 0, in which case the 0 constant term is displayed). Addition of terms with negative coefficients are replaced by subtraction of terms with positive coefficients except for the first displayed term (i.e. we display -3 for a constant negative polynomial, but 1 - 3 x + x^2 if the negative coefficient is not the first one displayed).

Overrides:

toString in class Object

Returns:

a string representation of the polynomial.

hashCode

public int hashCode()

Overrides:

hashCode in class Object

equals

public boolean equals(Object obj)

Overrides:

equals in class Object