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Re: invfreqs -- specifying numerator without independant term

From: Doug Stewart
Subject: Re: invfreqs -- specifying numerator without independant term
Date: Wed, 22 Sep 2010 10:57:50 -0400

On Wed, Sep 22, 2010 at 10:17 AM, CdeMills <address@hidden> wrote:
> Hello,
> I'm trying to identify a frequency response of the form
> H(s) = (b2 s^2 + b1 s) / (1+a1 s)
> The specific problem is thus that the numerator has only two degrees of
> freedom. When I generate the frequency response using H(s) = freqs(B, A, w)
> then try to get back coefficients values through invfreqs, it fails as the
> equation system is singular. Is there some way to reformulate the problem to
> get around this missing term ?
> Regards
> Pascal
> --
> View this message in context: 
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One idea that I use in control theory is to add a pole at a much
higher frequency. This makes the math work and doesn't change the
response at the low frequencies

try adding a pole say:

s + 1000

 I hope this helps.

Doug Stewart

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