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   -> Volume 2, Issue 5

Reply: Question concerning Numerical Recipes software WD 2.4 #9
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Arnold G. Gill

PostPosted: Fri Nov 29, 2002 2:28 pm    
Subject: Reply: Question concerning Numerical Recipes software WD 2.4 #9
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Reply: Question concerning Numerical Recipes software WD 2.4 #9

Note from the editor: this is a reply to the question posed in
Wavelet Digest 2.4, topip #9. The original question is repeated here.

Guru Prasad writes:

>I got through ananymous ftp, thanks to W. Press, software in FORTRAN
>for 1-d (vector) and 2-d (matrices) wavelet transforms. It has 2 options
>i) D4 wavelets or
>ii) D4, D12 or D20 wavelets
>When I try using these programs to wavelet transform matrices, I get
>different results from D4 of (i) which used subroutine DAUB4 explicitly
>and from D4 option of (ii) where user has to preset the wavelets he wants.
>I am puzzeled about this unable to figure out some thing wrong
>in my using the code or understanding or bug in one of the options
>Any comments from whoever experienced with these softwares?

I discovered this when I tried his routines over two years ago. At
that time, I noticed that the coefficients in the two routines are
rotated in a slightly different manner. I compared the routines to the
defining equations and fixed the appropriate subroutine (can't remember
which one it was). I sent Press a note, got an acknowledgement from him
and uploaded the corrected routines to him. I don't know if this is the
same problem that you are experiencing now, but I would be very
disappointed if Press hadn't corrected the routines after having the
very minor error pointed out to him years ago.

So that is my advice - check the rotation of the coefficients,
using a Dirac signal. That should help you to clear things up.

Arnold G. Gill,
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