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? Thanks in advance. PS: I have written a 3D DCT in APL 10 years ago (and a FFT 25 years ago but I don't recover this APL FFT program!). DCT=Discrete Cosinus Transform that works also in the real domain instead of the complex one. 3D is 3 dimensions (2 dimensions + time) 3D DCT is used in compressing a lot images of a movie where the successive images are near the same (many 0's in the 3D DCT ).
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