Curve fitting: Komplex Inputdata -> curvefitting -> rationale polynom

[RRapha]

Hello,

i want to curvefit measured Frequency-Response data to a rationale polynom

(Transfer function ). Something like "invreqs" for Mathscript-node. Does anybody

know a VI for this? The nonlinear-curvefit.VI for example doesn´t support komplex input.

Thx for any help!!

Greetings

RRapha

[Ken_Tobler]

Hi!

At the time there isn't any VI which directly calculate the curve fit from complex curves

Best regards
Ken

[altenbach]

Of course you could just create a normal (non complex) array from your data by creating a real array that contains the real and imaginary parts interleaved (easiest by using typecast) and is twice as long. Now use nonlinear curve fit (vi model) and write the model in such a way that it produces the interleaved output to be compared with the interleaved raw data array.

I don't know how well that will work but shouldn't be too hard to try. What is your model function?

In general, rational functions (the term "rational polynominal" is discouraged, see http://mathworld.wolfram.com/RationalPolynomial.html) could pose a fitting problem due to the possible presence of poles.