jnt.FFT

Class RealFloatFFT

java.lang.Object

jnt.FFT.RealFloatFFT

Direct Known Subclasses:

RealFloatFFT_Radix2

public abstract class RealFloatFFT
extends Object

Abstract Class representing FFT's of real, single precision data. Concrete classes are typically named RealFloatFFT_method, implement the FFT using some particular method.

The physical layout of the mathematical data d[i] in the array data is as follows:

    d[i] = data[i0 + stride*i]

The FFT (D[i]) of real data (d[i]) is complex, but restricted by symmetry:

    D[n-i] = conj(D[i])

It turns out that there are still n `independent' values, so the transformation can still be carried out in-place. However, each Real FFT method tends to leave the real and imaginary parts distributed in the data array in its own unique arrangment.

You must consult the documentation for the specific classes implementing RealFloatFFT for the details. Note, however, that each class's backtransform and inverse methods understand thier own unique ordering of the transformed result and can invert it correctly.

Author:

Bruce R. Miller bruce.miller@nist.gov, Contribution of the National Institute of Standards and Technology,, not subject to copyright.

Constructor Summary

Constructors

Constructor and Description
RealFloatFFT(int n) Create an FFT for transforming n points of real, single precision data.

Method Summary

Methods

Modifier and Type	Method and Description
void	backtransform(float[] data) Compute the (unnomalized) inverse FFT of data, leaving it in place.
abstract void	backtransform(float[] data, int i0, int stride) Compute the (unnomalized) inverse FFT of data, leaving it in place.
protected void	checkData(float[] data, int i0, int stride)
void	inverse(float[] data) Compute the (nomalized) inverse FFT of data, leaving it in place.
void	inverse(float[] data, int i0, int stride) Compute the (nomalized) inverse FFT of data, leaving it in place.
float	normalization() Return the normalization factor.
float[]	toWraparoundOrder(float[] data) Return data in wraparound order.
abstract float[]	toWraparoundOrder(float[] data, int i0, int stride) Return data in wraparound order.
void	transform(float[] data) Compute the Fast Fourier Transform of data leaving the result in data.
abstract void	transform(float[] data, int i0, int stride) Compute the Fast Fourier Transform of data leaving the result in data.

Methods inherited from class java.lang.Object

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

Constructor Detail

RealFloatFFT

public RealFloatFFT(int n)

Create an FFT for transforming n points of real, single precision data.

Method Detail

checkData

protected void checkData(float[] data,
             int i0,
             int stride)

transform

public void transform(float[] data)

Compute the Fast Fourier Transform of data leaving the result in data.

transform

public abstract void transform(float[] data,
             int i0,
             int stride)

Compute the Fast Fourier Transform of data leaving the result in data.

toWraparoundOrder

public float[] toWraparoundOrder(float[] data)

Return data in wraparound order.

See Also:

wraparound format

toWraparoundOrder

public abstract float[] toWraparoundOrder(float[] data,
                        int i0,
                        int stride)

Return data in wraparound order. i0 and stride are used to traverse data; the new array is in packed (i0=0, stride=1) format.

See Also:

wraparound format

backtransform

public void backtransform(float[] data)

Compute the (unnomalized) inverse FFT of data, leaving it in place.

backtransform

public abstract void backtransform(float[] data,
                 int i0,
                 int stride)

Compute the (unnomalized) inverse FFT of data, leaving it in place.

normalization

public float normalization()

Return the normalization factor. Multiply the elements of the backtransform'ed data to get the normalized inverse.

inverse

public void inverse(float[] data)

Compute the (nomalized) inverse FFT of data, leaving it in place.

inverse

public void inverse(float[] data,
           int i0,
           int stride)

Compute the (nomalized) inverse FFT of data, leaving it in place.