JSci.maths.FourierMath Maven / Gradle / Ivy
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JSci is a set of open source Java packages. The aim is to encapsulate scientific methods/principles in the most natural way possible. As such they should greatly aid the development of scientific based software.
It offers: abstract math interfaces, linear algebra (support for various matrix and vector types), statistics (including probability distributions), wavelets, newtonian mechanics, chart/graph components (AWT and Swing), MathML DOM implementation, ...
Note: some packages, like javax.comm, for the astro and instruments package aren't listed as dependencies (not available).
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package JSci.maths;
/**
* The Fourier math library.
* This class cannot be subclassed or instantiated because all methods are static.
* Use sort(transform(sort(...))) for the discrete analogue of the continuous Fourier transform,
* and sort(inverseTransform(sort(...))) for the inverse transform.
* @jsci.planetmath FourierTransform
* @version 0.9
* @author Mark Hale
*/
public final class FourierMath extends AbstractMath implements NumericalConstants {
private FourierMath() {}
/**
* Fourier transform (2Pi convention).
* @param data an array containing the positive time part of the signal
* followed by the negative time part.
* @return an array containing positive frequencies in ascending order
* followed by negative frequencies in ascending order.
* @author Don Cross
*/
public static Complex[] transform(final Complex data[]) {
final int N=data.length;
if(!isPowerOf2(N))
throw new IllegalArgumentException("The number of samples must be a power of 2.");
final double arrayRe[]=new double[N];
final double arrayIm[]=new double[N];
final int numBits=numberOfBitsNeeded(N);
// Simultaneous data copy and bit-reversal ordering into output
for(int i=0;i0)
return i;
}
}
/**
* Reverse bits.
* @author Don Cross
*/
private static int reverseBits(int index,final int numBits) {
int i,rev;
for(i=rev=0;i>=1;
}
return rev;
}
/**
* Sorts the output from the Fourier transfom methods into
* ascending frequency/time order.
*/
public static Complex[] sort(final Complex output[]) {
final Complex ret[]=new Complex[output.length];
final int Nby2=output.length/2;
for(int i=0;i