org.das2.qds.math.fft.jnt

Class ComplexDoubleFFT

java.lang.Object

org.das2.qds.math.fft.jnt.ComplexDoubleFFT

Direct Known Subclasses:

ComplexDoubleFFT_Mixed

public abstract class ComplexDoubleFFT
extends java.lang.Object

Abstract Class representing FFT's of complex, double precision data. Concrete classes are typically named ComplexDoubleFFT_method, implement the FFT using some particular method.

Complex data is represented by 2 double values in sequence: the real and imaginary parts. Thus, in the default case (i0=0, stride=2), N data points is represented by a double array dimensioned to 2*N. To support 2D (and higher) transforms, an offset, i0 (where the first element starts) and stride (the distance from the real part of one value, to the next: at least 2 for complex values) can be supplied. The physical layout in the array data, of the mathematical data d[i] is as follows:

    Re(d[i]) = data[i0 + stride*i]
    Im(d[i]) = data[i0 + stride*i+1]

The transformed data is returned in the original data array in wrap-around order.

Constructor Summary

Constructors

Constructor and Description
ComplexDoubleFFT(int n) Create an FFT for transforming n points of complex, double precision data.

Method Summary

Modifier and Type	Method and Description
void	backtransform(ComplexArray.Double data)
abstract void	backtransform(ComplexArray.Double data, int i0, int stride) Compute the (unnomalized) inverse FFT of data, leaving it in place.
protected void	checkData(ComplexArray.Double data, int i0, int stride)
ComplexDoubleFFT	getInstance(int n) Creates an instance of a subclass of ComplexDoubleFFT appropriate for data of n elements.
void	inverse(ComplexArray.Double data) Compute the (normalized) inverse FFT of data, leaving it in place.
double	normalization() Return the normalization factor.
void	transform(ComplexArray.Double data) Compute the Fast Fourier Transform of data leaving the result in data.
abstract void	transform(ComplexArray.Double 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

ComplexDoubleFFT

public ComplexDoubleFFT(int n)

Create an FFT for transforming n points of complex, double precision data.

Method Detail

getInstance

public ComplexDoubleFFT getInstance(int n)

Creates an instance of a subclass of ComplexDoubleFFT appropriate for data of n elements.

checkData

protected void checkData(ComplexArray.Double data,
                         int i0,
                         int stride)

transform

public void transform(ComplexArray.Double data)

Compute the Fast Fourier Transform of data leaving the result in data. The array data must be dimensioned (at least) 2*n, consisting of alternating real and imaginary parts.

transform

public abstract void transform(ComplexArray.Double data,
                               int i0,
                               int stride)

Compute the Fast Fourier Transform of data leaving the result in data. The array data must contain the data points in the following locations:

    Re(d[i]) = data[i0 + stride*i]
    Im(d[i]) = data[i0 + stride*i+1]

backtransform

public void backtransform(ComplexArray.Double data)

backtransform

public abstract void backtransform(ComplexArray.Double data,
                                   int i0,
                                   int stride)

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

normalization

public double normalization()

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

inverse

public void inverse(ComplexArray.Double data)

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