Michel Dumontier wrote: > I have used Huffman compression in J using > http://www.jsoftware.com/jwiki/Essays/Huffman%20Coding > It works very well. But nothing to do with FHT that transforms time in > frequency. (in real numbers not like FFT that gives complex numbers). > There is nothing on JWiki Essays on FFT or FHT or other time<=> frequency > transforms. (FHT=Fast Hartley Transform which is faster than FFT). > Could somebody provide me such algorithms in APL or/and J ? > Is there a faster transform than the Hartley's one? >
FFTW is provided as a J add-on (Windows only). It is common wisdom that writing your own FFT is difficult. You can do a slow (linear algebra) DFT along the lines suggested in http://www.jsoftware.com/jwiki/JohnRandall/FourierTransformAndPolynomialMultiplication Using a specialized form of the FFT may be better than using the Hartley transformation, simply because the FFT has received more attention. I doubt there is anything asymptotically faster. If you are interested in the DCT for image compression, I suggest you look at JPEG compression: DCT is the algorithm that is used. Best wishes, John ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
