1 ! Copyright (c) 2008 Slava Pestov, Aaron Schaefer.
2 ! See http://factorcode.org/license.txt for BSD license.
3 USING: assocs columns grouping kernel math math.statistics math.vectors
5 IN: math.transforms.haar
7 ! Haar Wavelet Transform -- http://dmr.ath.cx/gfx/haar/
11 : averages ( seq -- seq' )
14 : differences ( seq averages -- differences )
15 [ 0 <column> ] dip v- ;
17 : haar-step ( seq -- differences averages )
18 2 group dup averages [ differences ] keep ;
20 : rev-haar-step ( seq -- seq )
21 halves [ v+ ] [ v- ] 2bi zip concat ;
25 : haar ( seq -- seq' )
26 dup length 1 <= [ haar-step haar prepend ] unless ;
28 : rev-haar ( seq -- seq' )
29 dup length 2 > [ halves swap rev-haar prepend ] when rev-haar-step ;