org.apache.commons.math.transform

## Class FastFourierTransformer.RootsOfUnity

- java.lang.Object
- - org.apache.commons.math.transform.FastFourierTransformer.RootsOfUnity

All Implemented Interfaces:
  java.io.Serializable

Enclosing class:
  FastFourierTransformer

    private static class FastFourierTransformer.RootsOfUnity
    extends java.lang.Object
    implements java.io.Serializable

Computes the nth roots of unity. A cache of already computed values is maintained.

### Field Summary

Fields
`private boolean` `isForward` Forward/reverse indicator.
`private int` `omegaCount` Number of roots of unity.
`private double[]` `omegaImaginaryForward` Imaginary part of the roots for forward transform.
`private double[]` `omegaImaginaryInverse` Imaginary part of the roots for reverse transform.
`private double[]` `omegaReal` Real part of the roots.
`private static long` `serialVersionUID` Serializable version id.

### Constructor Summary

Constructors
Constructor and Description
`FastFourierTransformer.RootsOfUnity()` Build an engine for computing then th roots of unity

### Method Summary

Methods
`void` `computeOmega(int n)` Computes the nth roots of unity.
`double` `getOmegaImaginary(int k)` Get the imaginary part of the kth nth root of unity
`double` `getOmegaReal(int k)` Get the real part of the kth nth root of unity
`boolean` `isForward()` Check if computation has been done for forward or reverse transform.

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

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

### Field Detail

#### serialVersionUID

    private static final long serialVersionUID

Serializable version id.

See Also:
  Constant Field Values

#### omegaCount

    private int omegaCount

Number of roots of unity.

#### omegaReal

    private double[] omegaReal

Real part of the roots.

#### omegaImaginaryForward

    private double[] omegaImaginaryForward

Imaginary part of the roots for forward transform.

#### omegaImaginaryInverse

    private double[] omegaImaginaryInverse

Imaginary part of the roots for reverse transform.

#### isForward

    private boolean isForward

Forward/reverse indicator.

### Constructor Detail

#### FastFourierTransformer.RootsOfUnity

    public FastFourierTransformer.RootsOfUnity()

Build an engine for computing then th roots of unity

### Method Detail

#### isForward

    public boolean isForward()
                      throws java.lang.IllegalStateException

Check if computation has been done for forward or reverse transform.

Returns:
  true if computation has been done for forward transform
Throws:
  `java.lang.IllegalStateException` - if no roots of unity have been computed yet

#### computeOmega

    public void computeOmega(int n)
                      throws java.lang.IllegalArgumentException

Computes the nth roots of unity.

The computed omega[] = { 1, w, w2, ... w(n-1) } where w = exp(-2 π i / n), i = &sqrt;(-1).

Note that n is positive for forward transform and negative for inverse transform.

Parameters:
  `n` - number of roots of unity to compute, positive for forward transform, negative for inverse transform
Throws:
  `java.lang.IllegalArgumentException` - if n = 0

#### getOmegaReal

    public double getOmegaReal(int k)
                        throws java.lang.IllegalStateException,
                               java.lang.IllegalArgumentException

Get the real part of the kth nth root of unity

Parameters:
  `k` - index of the nth root of unity
Returns:
  real part of the kth nth root of unity
Throws:
  `java.lang.IllegalStateException` - if no roots of unity have been computed yet
  `java.lang.IllegalArgumentException` - if k is out of range

#### getOmegaImaginary

    public double getOmegaImaginary(int k)
                             throws java.lang.IllegalStateException,
                                    java.lang.IllegalArgumentException

Get the imaginary part of the kth nth root of unity

Parameters:
  `k` - index of the nth root of unity
Returns:
  imaginary part of the kth nth root of unity
Throws:
  `java.lang.IllegalStateException` - if no roots of unity have been computed yet
  `java.lang.IllegalArgumentException` - if k is out of range