ca.uol.aig.fftpack
Class RealDoubleFFT_Even

java.lang.Object
  extended byca.uol.aig.fftpack.RealDoubleFFT_Mixed
      extended byca.uol.aig.fftpack.RealDoubleFFT_Even

public class RealDoubleFFT_Even
extends ca.uol.aig.fftpack.RealDoubleFFT_Mixed

cosine FFT transform of a real even sequence.


Field Summary
 double norm_factor
          norm_factor can be used to normalize this FFT transform.
 
Constructor Summary
RealDoubleFFT_Even(int n)
          Construct a wavenumber table with size n.
 
Method Summary
 void bt(double[] x)
          Backward cosine FFT transform.
 void ft(double[] x)
          Forward cosine FFT transform.
 
Methods inherited from class java.lang.Object
equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

norm_factor

public double norm_factor
norm_factor can be used to normalize this FFT transform. This is because a call of forward transform (ft) followed by a call of backward transform (bt) will multiply the input sequence by norm_factor.

Constructor Detail

RealDoubleFFT_Even

public RealDoubleFFT_Even(int n)
Construct a wavenumber table with size n. The sequences with the same size can share a wavenumber table. The prime factorization of n together with a tabulation of the trigonometric functions are computed and stored.

Parameters:
n - the size of a real data sequence. When (n-1) is a multiplication of small numbers (4, 2, 3, 5), this FFT transform is very efficient.
Method Detail

ft

public void ft(double[] x)
Forward cosine FFT transform. It computes the discrete sine transform of an odd sequence.

Parameters:
x - an array which contains the sequence to be transformed. After FFT, x contains the transform coeffients.

bt

public void bt(double[] x)
Backward cosine FFT transform. It is the unnormalized inverse transform of ft.

Parameters:
x - an array which contains the sequence to be transformed. After FFT, x contains the transform coeffients.