Example usage for org.apache.commons.math3.transform TransformType INVERSE

Introduction

In this page you can find the example usage for org.apache.commons.math3.transform TransformType INVERSE.

Prototype

TransformType INVERSE

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Document

The type to be specified for inverse transforms.

Usage

From source file:com.github.jonmarsh.waveform_processing_for_imagej.WaveformUtils.java

/**
 * Computes discrete Hilbert transform of the input array (in place) using
 * FFTs. The transform operation is computed in place. For efficiency, no
 * error checking is performed on input data range limits or length of input
 * array. The input array length <b>must</b> be equal to a power of 2,
 * otherwise a runtime exception may be thrown.
 *
 * @param a         input array//w w w. ja v  a 2s . c o  m
 * @param isForward true for forward Hilbert transform, false for inverse
 *                  Hilbert transform
 */
public static final void fastHilbertTransformPowerOf2(double[] a, boolean isForward) {
    int n = a.length;
    int nOver2 = n / 2;
    double c = isForward ? 1.0 : -1.0;

    // create zero-valued imaginary component
    double[] aIm = new double[n];

    // perform FFT
    FastFourierTransformer.transformInPlace(new double[][] { a, aIm }, DftNormalization.STANDARD,
            TransformType.FORWARD);

    // zero out DC and Nyquist components
    a[0] = aIm[0] = a[nOver2] = aIm[nOver2] = 0.0;

    // multiply positive frequency components by -I
    for (int i = 1; i < nOver2; i++) {
        double temp = a[i];
        a[i] = c * aIm[i];
        aIm[i] = -c * temp;
    }

    // multiply negative frequency components by I
    for (int i = nOver2 + 1; i < n; i++) {
        double temp = a[i];
        a[i] = -c * aIm[i];
        aIm[i] = c * temp;
    }

    FastFourierTransformer.transformInPlace(new double[][] { a, aIm }, DftNormalization.STANDARD,
            TransformType.INVERSE);
}

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From source file:com.github.jonmarsh.waveform_processing_for_imagej.WaveformUtils.java

/**
 * Filters input array within specified range by Fourier transforming the
 * segment of the input array, multiplying the real and imaginary parts of
 * the transformed segment by {@code filterCoefficients} element-by-element,
 * and inverse Fourier transforming the result. The output is the filtered
 * segment; input array is unchanged. The length of the segment to be
 * filtered <b>must</b> be a power-of-2, otherwise unexpected results or
 * runtime errors may occur. No error checking is performed on range limits;
 * if the values are negative or outside the range of the array, a runtime
 * exception may be thrown./*from  ww w.j  a v a 2s  .  co m*/
 *
 * @param a                  input array (assumed to be real-valued)
 * @param from               initial index of the range of elements to
 *                           filter
 * @param to                 final index of the range of elements to filter
 * @param filterCoefficients frequency-domain filter coefficients; if length
 *                           of array is not equal to {@code from-to},
 *                           return an unmodified copy of the input array
 *                           segment
 * @return filtered array segment
 */
public static final double[] freqDomainFilter(double[] a, int from, int to, double[] filterCoefficients) {
    int n = to - from;

    double[] re = Arrays.copyOfRange(a, from, to);
    if (filterCoefficients.length != n) {
        return re;
    }

    double[] im = new double[n];

    FastFourierTransformer.transformInPlace(new double[][] { re, im }, DftNormalization.STANDARD,
            TransformType.FORWARD);
    for (int i = 0; i < n; i++) {
        re[i] *= filterCoefficients[i];
        im[i] *= filterCoefficients[i];
    }
    FastFourierTransformer.transformInPlace(new double[][] { re, im }, DftNormalization.STANDARD,
            TransformType.INVERSE);

    return re;
}

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From source file:org.hawkular.datamining.forecast.utils.AutomaticPeriodIdentificationTest.java

/**
 *
 * http://stackoverflow.com/questions/12239096/computing-autocorrelation-with-fft-using-jtransforms-library
 * http://dsp.stackexchange.com/questions/3337/finding-peaks-in-an-autocorrelation-function
 * @throws IOException/*from   w  w w .j a v a2  s .co  m*/
 */
//    @Test
public void testFFT() throws IOException {

    ModelData rModel = ModelReader.read("austourists");
    double[] x = Utils.toArray(rModel.getData());

    FastFourierTransformer fft = new FastFourierTransformer(DftNormalization.STANDARD);

    Complex[] forward = fft.transform(x, TransformType.FORWARD);
    Complex[] inverse = fft.transform(forward, TransformType.INVERSE);
}

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