## org.apache.commons.math.analysis.polynomials
Class PolynomialFunctionLagrangeForm

    java.lang.Object
      org.apache.commons.math.analysis.polynomials.PolynomialFunctionLagrangeForm

All Implemented Interfaces:
  UnivariateRealFunction

    public class PolynomialFunctionLagrangeForm

extends java.lang.Object
implements UnivariateRealFunction

Implements the representation of a real polynomial function in Lagrange Form. For reference, see Introduction to Numerical Analysis, ISBN 038795452X, chapter 2.

The approximated function should be smooth enough for Lagrange polynomial to work well. Otherwise, consider using splines instead.

Since:
  1.2
Version:
  $Revision: 922708 $ $Date: 2010-03-13 20:15:47 -0500 (Sat, 13 Mar 2010) $

Field Summary
`private double[]` `coefficients` The coefficients of the polynomial, ordered by degree -- i.e.
`private boolean` `coefficientsComputed` Whether the polynomial coefficients are available.
`private double[]` `x` Interpolating points (abscissas).
`private double[]` `y` Function values at interpolating points.

Constructor Summary
`PolynomialFunctionLagrangeForm(double[] x, double[] y)` Construct a Lagrange polynomial with the given abscissas and function values.

Method Summary
`protected void` `computeCoefficients()` Calculate the coefficients of Lagrange polynomial from the interpolation data.
`int` `degree()` Returns the degree of the polynomial.
`static double` `evaluate(double[] x, double[] y, double z)` Evaluate the Lagrange polynomial using Neville's Algorithm.
`double[]` `getCoefficients()` Returns a copy of the coefficients array.
`double[]` `getInterpolatingPoints()` Returns a copy of the interpolating points array.
`double[]` `getInterpolatingValues()` Returns a copy of the interpolating values array.
`double` `value(double z)` Calculate the function value at the given point.
`static void` `verifyInterpolationArray(double[] x, double[] y)` Verifies that the interpolation arrays are valid.

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Field Detail

### coefficients

    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.

### x

    private final double[] x

  Interpolating points (abscissas).

### y

    private final double[] y

  Function values at interpolating points.

### coefficientsComputed

    private boolean coefficientsComputed

  Whether the polynomial coefficients are available.

Constructor Detail

### PolynomialFunctionLagrangeForm

    public PolynomialFunctionLagrangeForm(double[] x,
                                          double[] y)
                                   throws java.lang.IllegalArgumentException

  Construct a Lagrange polynomial with the given abscissas and function values. The order of interpolating points are not important.

  The constructor makes copy of the input arrays and assigns them.

  Parameters:
    `x` - interpolating points
    `y` - function values at interpolating points
  Throws:
    `java.lang.IllegalArgumentException` - if input arrays are not valid

Method Detail

### value

    public double value(double z)
                 throws FunctionEvaluationException

  Calculate the function value at the given point.

  Specified by:
    `value` in interface `UnivariateRealFunction`
  Parameters:
    `z` - the point at which the function value is to be computed
  Returns:
    the function value
  Throws:
    `FunctionEvaluationException` - if a runtime error occurs
  See Also:
    `UnivariateRealFunction.value(double)`

### degree

    public int degree()

  Returns the degree of the polynomial.

  Returns:
    the degree of the polynomial

### getInterpolatingPoints

    public double[] getInterpolatingPoints()

  Returns a copy of the interpolating points array.

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

  Returns:
    a fresh copy of the interpolating points array

### getInterpolatingValues

    public double[] getInterpolatingValues()

  Returns a copy of the interpolating values array.

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

  Returns:
    a fresh copy of the interpolating values array

### getCoefficients

    public double[] getCoefficients()

  Returns a copy of the coefficients array.

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

  Note that coefficients computation can be ill-conditioned. Use with caution and only when it is necessary.

  Returns:
    a fresh copy of the coefficients array

### evaluate

    public static double evaluate(double[] x,
                                  double[] y,
                                  double z)
                           throws DuplicateSampleAbscissaException,
                                  java.lang.IllegalArgumentException

  Evaluate the Lagrange polynomial using Neville's Algorithm. It takes O(N^2) time.

  This function is made public static so that users can call it directly without instantiating PolynomialFunctionLagrangeForm object.

  Parameters:
    `x` - the interpolating points array
    `y` - the interpolating values array
    `z` - the point at which the function value is to be computed
  Returns:
    the function value
  Throws:
    `DuplicateSampleAbscissaException` - if the sample has duplicate abscissas
    `java.lang.IllegalArgumentException` - if inputs are not valid

### computeCoefficients

    protected void computeCoefficients()
                                throws java.lang.ArithmeticException

  Calculate the coefficients of Lagrange polynomial from the interpolation data. It takes O(N^2) time.

  Note this computation can be ill-conditioned. Use with caution and only when it is necessary.

  Throws:
    `java.lang.ArithmeticException` - if any abscissas coincide

### verifyInterpolationArray

    public static void verifyInterpolationArray(double[] x,
                                                double[] y)
                                         throws java.lang.IllegalArgumentException

  Verifies that the interpolation arrays are valid.

  The arrays features checked by this method are that both arrays have the same length and this length is at least 2.

  The interpolating points must be distinct. However it is not verified here, it is checked in evaluate() and computeCoefficients().

  Parameters:
    `x` - the interpolating points array
    `y` - the interpolating values array
  Throws:
    `java.lang.IllegalArgumentException` - if not valid
  See Also:
    `evaluate(double[], double[], double)`, `computeCoefficients()`

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