Welcome to the Java Programming Forums


The professional, friendly Java community. 21,500 members and growing!


The Java Programming Forums are a community of Java programmers from all around the World. Our members have a wide range of skills and they all have one thing in common: A passion to learn and code Java. We invite beginner Java programmers right through to Java professionals to post here and share your knowledge. Become a part of the community, help others, expand your knowledge of Java and enjoy talking with like minded people. Registration is quick and best of all free. We look forward to meeting you.


>> REGISTER NOW TO START POSTING


Members have full access to the forums. Advertisements are removed for registered users.

Results 1 to 2 of 2

Thread: FFT code

  1. #1
    Junior Member
    Join Date
    Apr 2013
    Posts
    1
    Thanks
    0
    Thanked 0 Times in 0 Posts

    Default FFT code

    Hi,
    Im a beginner and can't quite figure out how this class works out the FFT...Please help
     
    final public class FFT {
     
        private int size = 0;
        private boolean valid = false;
        private Complex[] in_data = null,  out_data = null;
        private Vector<FFTPrecalc> fftPrecalc;
        FFTPrecalc tcalc;
        private final double pi2 = Math.PI * 2.0;
        private double scale;
        private double fft_pi2;
        private boolean inverse;
     
        public FFT() {
        }
     
        boolean test_pwr2(int n) {
            return (n >= 2 && ((n & (n - 1)) == 0));
        }
     
        int rev_bits(int index, int size) {
            int rev = 0;
            for (; size > 1; size >>= 1) {
                rev = (rev << 1) | (index & 1);
                index >>= 1;
            }
            return rev;
        }
     
        public void initialize(int n, boolean inverse) {
            this.inverse = inverse;
            Complex tc;
            fft_pi2 = (inverse) ? -pi2 : pi2;
            try {
                if (size != n) {
                    if (!test_pwr2(n)) {
                        throw (new Exception("Error: array size is not a power of 2\n"));
                    } else {
                        size = n;
                        valid = true;
                        in_data = new Complex[n];
                        out_data = new Complex[n];
                        scale = 1.0 / size;
                        int rb;
                        for (int i = 0; i < n; i++) {
                            tc = new Complex();
                            rb = rev_bits(i, n);
                            in_data[i] = tc;
                            out_data[rb] = tc;
                        }
                        fftPrecalc = new Vector<FFTPrecalc>();
     
                        int imax = 1;
                        while(imax < size) {
                            tcalc = new FFTPrecalc(imax,fft_pi2);
                            fftPrecalc.add(tcalc);
                            imax = tcalc.istep;
                        }
                    }
                }
     
            } catch (Exception e) {
                System.out.println(getClass().getName() + ": Error: " + e);
            }
        }
     
        void resize(int n, boolean inverse) {
            initialize(n, inverse);
        }
     
        boolean valid() {
            return valid;
        }
     
        int size() {
            return size;
        }
     
        public Complex[] inputArray() {
            return in_data;
        }
     
        public Complex[] outputArray() {
            return out_data;
        }
     
        void fft1() {
            if (valid && out_data != null) {
                int imax, istep, m, i, j, k;
                double wtemp, wr, wpr, wpi, wi, theta;
                Complex ac, bc;
                Complex tc = new Complex();
                FFTPrecalc t;
                Iterator<FFTPrecalc> it = fftPrecalc.iterator();
                // Danielson-Lanzcos method
                // with some precomputation
                while (it.hasNext()) {
                    tcalc = it.next();
                    imax = tcalc.imax;
                    istep = tcalc.istep;
                    wpr = tcalc.wpr;
                    wpi = tcalc.wpi;
                    wr = 1.0;
                    wi = 0.0;
                    for (m = 0; m < imax; ++m) {
                        for (i = m; i < size; i += istep) {
                            j = i + imax;
                            ac = out_data[j];
                            bc = out_data[i];
                            tc.re = wr * ac.re - wi * ac.im;
                            tc.im = wr * ac.im + wi * ac.re;
                            ac.re = bc.re - tc.re;
                            ac.im = bc.im - tc.im;
                            bc.add(tc);
                        }
                        wr = (wtemp = wr) * wpr - wi * wpi + wr;
                        wi = wi * wpr + wtemp * wpi + wi;
                    }
                }
                if (!inverse) {
                    for (k = 0; k < size; k++) {
                        out_data[k].mult(scale);
                    }
                }
            }
        }
    }


  2. #2
    Super Moderator Norm's Avatar
    Join Date
    May 2010
    Location
    Eastern Florida
    Posts
    25,042
    Thanks
    63
    Thanked 2,708 Times in 2,658 Posts

    Default Re: FFT code

    how this class works out the FFT
    Please explain what your problem is. Which statements don't you understand?
    If you don't understand my answer, don't ignore it, ask a question.

Similar Threads

  1. Replies: 4
    Last Post: January 24th, 2013, 11:20 AM
  2. Replies: 7
    Last Post: January 24th, 2013, 10:41 AM
  3. Trouble Porting my Java File Reading Code to Android Code
    By Gravity Games in forum Android Development
    Replies: 0
    Last Post: December 6th, 2012, 04:38 PM
  4. Replies: 5
    Last Post: November 14th, 2012, 10:47 AM
  5. Replies: 3
    Last Post: September 3rd, 2012, 11:36 AM