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   -> Volume 7, Issue 5


Answer: Error in Matlab manual (WD 7.4 #26)
 
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Paul Costa (pc@mathworks.com)
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PostPosted: Tue Apr 21, 1998 8:37 pm    
Subject: Answer: Error in Matlab manual (WD 7.4 #26)
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#25 Answer: Error in Matlab manual (WD 7.4 #26)

Hello Wavelet Digest authors,

My name is Paul Costa and I work for The MathWorks. I would like to
answer a question which was posed in the Wavelet Digest, Vol. 07, Nr. 04.

Here is the question:

> Date: Sun, 12 Apr 1998 15:24:03 PKT
> From: "Awais M. Hussain" <awais.hussain@tes-cressoft.com.pk>
> Subject: #26 Question: Error in Matlab wavelet toolbox manual?
> Question:
> The MATLAB wavelet toolbox manual on p.6-13 (1996) defines the DWT
> of a signal s(n) as:
> C(j,k) = sum_{n in Z} s(n) g_{j,k} (n)
> with
> g_{j,k}(n) = 2^{-j/2} g( 2^{-j} n - k)
> where g(n) is the wavelet filter's impulse response (discrete-
> time). Thus g_{j,k} are the dilations of the discrete filter?
> This does not appear to be the correct representation of the DWT. Can
> someone explain?
> Awais

Here is the Answer:

There is a typographical error on page 6-13 of the Wavelet Toolbox
User's Guide (March 1996). This error was also present in the MATLAB
5.0 version of this User's Guide (1997) on page 6-14.

The correct equation for g_{j,k}(n) should read:

g_{j,k}(n) = 2^{j/2} g( 2^{j} n - k)

Paul Costa
The MathWorks, Inc.
pc@mathworks.com
All times are GMT + 1 Hour
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