A Sample Code: Getting a Real FFT of 1D array using jTransform library.

gistfile1.java

import edu.emory.mathcs.jtransforms.fft.DoubleFFT_1D;

public class FftTest {
    public static void main(String[] args) {
        double[] input = new double[]{
                0.0176,
                -0.0620,
                0.2467,
                0.4599,
                -0.0582,
                0.4694,
                0.0001,
                -0.2873};
        DoubleFFT_1D fftDo = new DoubleFFT_1D(input.length);
        double[] fft = new double[input.length * 2];
        System.arraycopy(input, 0, fft, 0, input.length);
        fftDo.realForwardFull(fft);

        for(double d: fft) {
            System.out.println(d);
        }
    }
}

thanks, for me this was a critical bit of info to get this working. just a few notes ...

1. import edu.emory.mathcs.jtransforms.fft.DoubleFFT_1D; is now at ...
   import org.jtransforms.fft.DoubleFFT_1D;
2. to compile the source you also need ...
   https://github.com/IcmVis/JLargeArrays
3. for me the resulting output for comparison is ...
   0.7862
   0.0
   -0.8283067304251197
   -0.3991936433800569
   -0.2874
   -0.2348
   0.9799067304251197
   0.09400635661994317
   -0.37379999999999997
   0.0
   0.9799067304251197
   -0.09400635661994317
   -0.2874
   0.2348
   -0.8283067304251197
   0.3991936433800569
4. to get back to the original data add...
   System.out.println("get back");
   fftDo.complexInverse(fft,true);
   for (double d: fft)
   System.out.println(d);

You are great!! Thank you for this sample!!

This is not entirely correct if you set a signal with a period T = 1 s, that is, the frequency should be 1 Hz, then with this code you will see 2 Hz. More correct would be DoubleFFT_1D fftDo = new DoubleFFT_1D(input.length / 2);