invfreqs and sensitivity

[Pascal A. Dupuis]

Hello,

I've measured an impedance at a number of frequencies, and I try to
model this using a pole-zero approach, that is:
1) let h by a vector of the complex impedances
2) let f be the set of frequencies
3) I use [Den, Num]= invfreqs(h, f, na, nb)

I also computed the variance of the impedance at each frequency, that
is, each complex value is also characterised by a (2, 2) covariance
matrix. I would like to use standard propagation technique to deduce a
covariance on the coefficients of the numerator and denominator. In
order to do so, I need the derivative of these coefficients with respect
to each value of h. Any idea of how to get an expression of such
derivatives without using numerical differentiation ?

Thanks in advance

Pascal Dupuis

-- 
Dr. ir. Pascal Dupuis
K. U. Leuven, ESAT/ELECTA (formerly ELEN):  http://www.esat.kuleuven.ac.be/
Kasteelpark Arenberg, 10; B-3001 Leuven-Heverlee, Belgium
Tel. +32-16-32 10 21 -- Fax +32-16-32 19 85



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