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Re: invfreqs -- specifying numerator without independant term


From: Moo
Subject: Re: invfreqs -- specifying numerator without independant term
Date: Wed, 22 Sep 2010 17:04:49 -0600

On Wed, Sep 22, 2010 at 8:17 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

I have no idea of the subject, but if it involves finding a solution to a singular linear system Ax=b, then you probably want a least-squares solution (closest approximation) by just doing x=A\b.  I imagine Doug's solution will give similar results, since it sounds like just making a small perturbation of your original system to make it nonsingular for numerical purposes.

If all this is hidden inside the 'invfreqs' function,

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