org.apache.commons.math3.analysis.polynomials

## Class PolynomialFunction

- java.lang.Object
- - org.apache.commons.math3.analysis.polynomials.PolynomialFunction

All Implemented Interfaces:
  Serializable, DifferentiableUnivariateFunction, UnivariateDifferentiableFunction, UnivariateFunction

    public class PolynomialFunction
    extends Object
    implements UnivariateDifferentiableFunction, DifferentiableUnivariateFunction, Serializable

Immutable representation of a real polynomial function with real coefficients.

Horner's Method is used to evaluate the function.

Version:
  $Id: PolynomialFunction.java 1383441 2012-09-11 14:56:39Z luc $
See Also:
  Serialized Form

### Nested Class Summary

Nested Classes
`static class` `PolynomialFunction.Parametric` Dedicated parametric polynomial class.

### Field Summary

Fields
`private double[]` `coefficients` The coefficients of the polynomial, ordered by degree -- i.e., coefficients[0] is the constant term and coefficients[n] is the coefficient of x^n where n is the degree of the polynomial.
`private static long` `serialVersionUID` Serialization identifier

### Constructor Summary

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

### Method Summary

Methods
`PolynomialFunction` `add(PolynomialFunction p)` Add a polynomial to the instance.
`int` `degree()` Returns the degree of the polynomial.
`UnivariateFunction` `derivative()` Returns the derivative as a `UnivariateFunction`.
`protected static double[]` `differentiate(double[] coefficients)` Returns the coefficients of the derivative of the polynomial with the given coefficients.
`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()`
`PolynomialFunction` `multiply(PolynomialFunction p)` Multiply the instance by a polynomial.
`PolynomialFunction` `negate()` Negate the instance.
`PolynomialFunction` `polynomialDerivative()` Returns the derivative as a `PolynomialFunction`.
`PolynomialFunction` `subtract(PolynomialFunction p)` Subtract a polynomial from the instance.
`String` `toString()` Returns a string representation of the polynomial.
`private static String` `toString(double coeff)` Creates a string representing a coefficient, removing ".0" endings.
`DerivativeStructure` `value(DerivativeStructure t)` Simple mathematical function.
`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`

### Field Detail

#### serialVersionUID

    private static final long serialVersionUID

Serialization identifier

See Also:
  Constant Field Values

#### coefficients

    private final double[] coefficients

The coefficients of the polynomial, ordered by degree -- i.e., coefficients[0] is the constant term and coefficients[n] is the coefficient of x^n where n is the degree of the polynomial.

### Constructor Detail

#### PolynomialFunction

    public PolynomialFunction(double[] c)
                       throws NullArgumentException,
                              NoDataException

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.
Throws:
  `NullArgumentException` - if `c` is `null`.
  `NoDataException` - if `c` is empty.

### 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]`

Specified by:
  `value` in interface `UnivariateFunction`
Parameters:
  `x` - Argument for which the function value should be computed.
Returns:
  the value of the polynomial at the given point.
See Also:
  `UnivariateFunction.value(double)`

#### 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)
                              throws NullArgumentException,
                                     NoDataException

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.
Throws:
  `NoDataException` - if `coefficients` is empty.
  `NullArgumentException` - if `coefficients` is `null`.

#### value

    public DerivativeStructure value(DerivativeStructure t)
                              throws NullArgumentException,
                                     NoDataException

Simple mathematical function.

`UnivariateDifferentiableFunction` classes compute both the value and the first derivative of the function.

Specified by:
  `value` in interface `UnivariateDifferentiableFunction`
Parameters:
  `t` - function input value
Returns:
  function result
Throws:
  `NoDataException` - if `coefficients` is empty.
  `NullArgumentException` - if `coefficients` is `null`.
Since:
  3.1

#### add

    public PolynomialFunction add(PolynomialFunction p)

Add a polynomial to the instance.

Parameters:
  `p` - Polynomial to add.
Returns:
  a new polynomial which is the sum of the instance and `p`.

#### subtract

    public PolynomialFunction subtract(PolynomialFunction p)

Subtract a polynomial from the instance.

Parameters:
  `p` - Polynomial to subtract.
Returns:
  a new polynomial which is the difference the instance minus `p`.

#### negate

    public PolynomialFunction negate()

Negate the instance.

Returns:
  a new polynomial.

#### multiply

    public PolynomialFunction multiply(PolynomialFunction p)

Multiply the instance by a polynomial.

Parameters:
  `p` - Polynomial to multiply by.
Returns:
  a new polynomial.

#### differentiate

    protected static double[] differentiate(double[] coefficients)
                                     throws NullArgumentException,
                                            NoDataException

Returns the coefficients of the derivative of the polynomial with the given coefficients.

Parameters:
  `coefficients` - Coefficients of the polynomial to differentiate.
Returns:
  the coefficients of the derivative or `null` if coefficients has length 1.
Throws:
  `NoDataException` - if `coefficients` is empty.
  `NullArgumentException` - if `coefficients` is `null`.

#### polynomialDerivative

    public PolynomialFunction polynomialDerivative()

Returns the derivative as a `PolynomialFunction`.

Returns:
  the derivative polynomial.

#### derivative

    public UnivariateFunction derivative()

Returns the derivative as a `UnivariateFunction`.

Specified by:
  `derivative` in interface `DifferentiableUnivariateFunction`
Returns:
  the derivative function.

#### 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.

#### toString

    private static String toString(double coeff)

Creates a string representing a coefficient, removing ".0" endings.

Parameters:
  `coeff` - Coefficient.
Returns:
  a string representation of `coeff`.

#### hashCode

    public int hashCode()

Overrides:
  `hashCode` in class `Object`

#### equals

    public boolean equals(Object obj)

Overrides:
  `equals` in class `Object`