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## Re: test this in matlab for my please

 From: Mike Miller Subject: Re: test this in matlab for my please Date: Fri, 8 Jul 2016 19:26:35 -0700 User-agent: Mutt/1.6.0 (2016-04-01)

```On Fri, Jul 08, 2016 at 22:01:03 -0400, Doug Stewart wrote:
> If you want to see what I have learned read this. It isn'e polished but
> does record
> the important points.
>
> https://dl.dropboxusercontent.com/u/24993484/Z_tran%20_of_repeated_roots.pdf
>
> I now have to rewrite my code to make it look better and then update the
> control pkg.
>
>
> There is one difference from matlab and as such one question.
> http://www.mathworks.com/help/signal/ref/impinvar.html
>
> matlab says;
>
> "
>
> Plot the digital impulse response, multiplying the numerator by a constant (
> Fs) to compensate for the 1/Fs gain introduced in the impulse response of
> the derived digital filter.
>
> [b,a] = butter(4,0.3,'s');
> [bz,az] = impinvar(b,a,10);
> sys = tf(b,a);
> impulse(sys);
> hold on;
> impz(10*bz,az,[],10);
>
> "
>
> Notice the 10*bz ;
>
> Their code produces the filter coefficients  that are wrong by a
> factor of Fs!!!!
>
> My code does not need this extra multiply by Fs.
>
> What should I do?
>
> To say it another way their output from the filter needs a correction factor!
>
> I would prefer to keep my results. It is derived with proper math.

Doug,

I haven't been following too closely since you've been mostly asking for
Matlab tests and I can't help with that.

Are you writing impinvar or are you working on impulse and comparing to
impinvar?

Are you aware that there already is an impinvar in the signal package?
Is that what you're asking about here?

I just don't want wasted duplicate effort if you didn't know that the
signal package already has an impinvar function. Maybe it needs
improvement or is not Matlab compatible, I'm not sure.

Cheers,

--
mike

```

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