invfreqs -- specifying numerator without independant term

[CdeMills]

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
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