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From:    at <tothlINF.U-SZEGED.HU>
Date:    Tue, 22 Jun 1999 10:13:00 MET

>From tothl Tue Jun 22 10:13:05 +0200 1999 remote from inf.u-szeged.hu
Date: Tue, 22 Jun 1999 10:13:05 +0200 (MET DST)
From: Toth Laszlo <tothl(at)inf.u-szeged.hu>
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Subject: Re: Cepstrum computation
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On Mon, 21 Jun 1999, Richard F. Lyon wrote:

> >                          C(t)=|| FFT( log( ||FFT(x)|| ) ) ||
> >
> >My question is: what happens when ||FFT(x)||=0 for some x?
> >Then we have to compute log(0), which is undefined (as we all know).
> >
> Yes, isn't it ridiculous that people sort of define things part way
> and then pretend they're OK?
>
Yes, ridiculous indeed. A mathematician would definitely add a comment like
"and if ||FFT(x)||=0 then ...".
When I wrote my first cepstrum code it took me many hours to figure out
why I get black lines in my images...
My solution was an if:

if(||FFT(x)||==0) { y=-BigNumber}
else {y=log(||FFT(x)||)

Where "BigNumber" is some big constant. Yes, it's terrible, but what could
have I done?

               Laszlo Toth
        Hungarian Academy of Sciences         *   "Military intelligence:
  Research Group on Artificial Intelligence   *    two words combined that
     e-mail: tothl(at)inf.u-szeged.hu            *    can't make sense"
     http://www.inf.u-szeged.hu/~tothl        *