Package org.apache.commons.math4.transform

Class FastFourierTransform

java.lang.Object

org.apache.commons.math4.transform.FastFourierTransform

All Implemented Interfaces:

Function<org.apache.commons.numbers.complex.Complex[],org.apache.commons.numbers.complex.Complex[]>, UnaryOperator<org.apache.commons.numbers.complex.Complex[]>, ComplexTransform

public class FastFourierTransform
extends Object
implements ComplexTransform

Implements the Fast Fourier Transform for transformation of one-dimensional real or complex data sets. For reference, see Applied Numerical Linear Algebra, ISBN 0898713897, chapter 6.

There are several variants of the discrete Fourier transform, with various normalization conventions, which are specified by the parameter FastFourierTransform.Norm.

The current implementation of the discrete Fourier transform as a fast Fourier transform requires the length of the data set to be a power of 2. This greatly simplifies and speeds up the code. Users can pad the data with zeros to meet this requirement. There are other flavors of FFT, for reference, see S. Winograd, On computing the discrete Fourier transform, Mathematics of Computation, 32 (1978), 175 - 199.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	FastFourierTransform.Norm	Normalization types.

Constructor Summary

Constructors

Constructor	Description
FastFourierTransform(FastFourierTransform.Norm normalization)
FastFourierTransform(FastFourierTransform.Norm normalization, boolean inverse)

Method Summary

Modifier and Type	Method	Description
org.apache.commons.numbers.complex.Complex[]	apply(double[] f)	Returns the transform of the specified data set.
org.apache.commons.numbers.complex.Complex[]	apply(DoubleUnaryOperator f, double min, double max, int n)	Returns the transform of the specified function.
org.apache.commons.numbers.complex.Complex[]	apply(org.apache.commons.numbers.complex.Complex[] f)	Returns the transform of the specified data set.
void	transformInPlace(double[][] dataRI)	Computes the standard transform of the data.

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.function.Function

andThen, compose

Constructor Detail

FastFourierTransform

public FastFourierTransform(FastFourierTransform.Norm normalization,
                            boolean inverse)

Parameters:

normalization - Normalization to be applied to the transformed data.

inverse - Whether to perform the inverse transform.

FastFourierTransform

public FastFourierTransform(FastFourierTransform.Norm normalization)

Parameters:

normalization - Normalization to be applied to the transformed data.

Method Detail

transformInPlace

public void transformInPlace(double[][] dataRI)

Computes the standard transform of the data. Computation is done in place. Assumed layout of the input data:

• dataRI[0][i]: Real part of the i-th data point,
• dataRI[1][i]: Imaginary part of the i-th data point.

Parameters:

dataRI - Two-dimensional array of real and imaginary parts of the data.

Throws:

IllegalArgumentException - if the number of data points is not a power of two, if the number of rows of the specified array is not two, or the array is not rectangular.

apply

public org.apache.commons.numbers.complex.Complex[] apply(double[] f)

Returns the transform of the specified data set.

Specified by:

apply in interface ComplexTransform

Parameters:

f - the data array to be transformed (signal).

Returns:

the transformed array (spectrum).

Throws:

IllegalArgumentException - if the length of the data array is not a power of two.

apply

public org.apache.commons.numbers.complex.Complex[] apply(DoubleUnaryOperator f,
                                                          double min,
                                                          double max,
                                                          int n)

Returns the transform of the specified function.

Specified by:

apply in interface ComplexTransform

Parameters:

f - Function to be sampled and transformed.

min - Lower bound (inclusive) of the interval.

max - Upper bound (exclusive) of the interval.

n - Number of sample points.

Returns:

the result.

Throws:

IllegalArgumentException - if the number of sample points n is not a power of two, if the lower bound is greater than, or equal to the upper bound, if the number of sample points n is negative

apply

public org.apache.commons.numbers.complex.Complex[] apply(org.apache.commons.numbers.complex.Complex[] f)

Returns the transform of the specified data set.

Specified by:

apply in interface ComplexTransform

Specified by:

apply in interface Function<org.apache.commons.numbers.complex.Complex[],org.apache.commons.numbers.complex.Complex[]>

Parameters:

f - the data array to be transformed (signal).

Returns:

the transformed array (spectrum).

Throws:

IllegalArgumentException - if the length of the data array is not a power of two.