org.apache.commons.math3.util

## Class ContinuedFraction

- java.lang.Object
- - org.apache.commons.math3.util.ContinuedFraction

    public abstract class ContinuedFraction
    extends java.lang.Object

Provides a generic means to evaluate continued fractions. Subclasses simply provided the a and b coefficients to evaluate the continued fraction.

References:

- Continued Fraction

Version:
  $Id: ContinuedFraction.java 1416643 2012-12-03 19:37:14Z tn $

### Field Summary

Fields
`private static double` `DEFAULT_EPSILON` Maximum allowed numerical error.

### Constructor Summary

Constructors
`protected` `ContinuedFraction()` Default constructor.

### Method Summary

Methods
`double` `evaluate(double x)` Evaluates the continued fraction at the value x.
`double` `evaluate(double x, double epsilon)` Evaluates the continued fraction at the value x.
`double` `evaluate(double x, double epsilon, int maxIterations)` Evaluates the continued fraction at the value x.
`double` `evaluate(double x, int maxIterations)` Evaluates the continued fraction at the value x.
`protected abstract double` `getA(int n, double x)` Access the n-th a coefficient of the continued fraction.
`protected abstract double` `getB(int n, double x)` Access the n-th b coefficient of the continued fraction.

### Methods inherited from class java.lang.Object

`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

### Field Detail

#### DEFAULT_EPSILON

    private static final double DEFAULT_EPSILON

Maximum allowed numerical error.

See Also:
  Constant Field Values

### Constructor Detail

#### ContinuedFraction

    protected ContinuedFraction()

Default constructor.

### Method Detail

#### getA

    protected abstract double getA(int n,
              double x)

Access the n-th a coefficient of the continued fraction. Since a can be a function of the evaluation point, x, that is passed in as well.

Parameters:
  `n` - the coefficient index to retrieve.
  `x` - the evaluation point.
Returns:
  the n-th a coefficient.

#### getB

    protected abstract double getB(int n,
              double x)

Access the n-th b coefficient of the continued fraction. Since b can be a function of the evaluation point, x, that is passed in as well.

Parameters:
  `n` - the coefficient index to retrieve.
  `x` - the evaluation point.
Returns:
  the n-th b coefficient.

#### evaluate

    public double evaluate(double x)
                    throws ConvergenceException

Evaluates the continued fraction at the value x.

Parameters:
  `x` - the evaluation point.
Returns:
  the value of the continued fraction evaluated at x.
Throws:
  `ConvergenceException` - if the algorithm fails to converge.

#### evaluate

    public double evaluate(double x,
                  double epsilon)
                    throws ConvergenceException

Evaluates the continued fraction at the value x.

Parameters:
  `x` - the evaluation point.
  `epsilon` - maximum error allowed.
Returns:
  the value of the continued fraction evaluated at x.
Throws:
  `ConvergenceException` - if the algorithm fails to converge.

#### evaluate

    public double evaluate(double x,
                  int maxIterations)
                    throws ConvergenceException,
                           MaxCountExceededException

Evaluates the continued fraction at the value x.

Parameters:
  `x` - the evaluation point.
  `maxIterations` - maximum number of convergents
Returns:
  the value of the continued fraction evaluated at x.
Throws:
  `ConvergenceException` - if the algorithm fails to converge.
  `MaxCountExceededException` - if maximal number of iterations is reached

#### evaluate

    public double evaluate(double x,
                  double epsilon,
                  int maxIterations)
                    throws ConvergenceException,
                           MaxCountExceededException

Evaluates the continued fraction at the value x.

The implementation of this method is based on the modified Lentz algorithm as described on page 18 ff. in:

- I. J. Thompson, A. R. Barnett. "Coulomb and Bessel Functions of Complex Arguments and Order." http://www.fresco.org.uk/papers/Thompson-JCP64p490.pdf

Note: the implementation uses the terms ai and bi as defined in Continued Fraction @ MathWorld.

Parameters:
  `x` - the evaluation point.
  `epsilon` - maximum error allowed.
  `maxIterations` - maximum number of convergents
Returns:
  the value of the continued fraction evaluated at x.
Throws:
  `ConvergenceException` - if the algorithm fails to converge.
  `MaxCountExceededException` - if maximal number of iterations is reached