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MathGroup Archive 1999

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Nonlinear Fit with complex model

  • To: mathgroup at
  • Subject: [mg19605] Nonlinear Fit with complex model
  • From: mtir at
  • Date: Sat, 4 Sep 1999 21:09:13 -0400
  • Sender: owner-wri-mathgroup at


I am trying to fit a data set of real values with
a model that involves complex numbers, i.e.
  model[a,b,c,d]=Abs[<complex expression in

When I am using NonlinearRegress (or
NonlinearFit) Mathematica complains that "One or
more derivatives of the model with respect to
parameters did not evaluate" and does not return a

I suspect that the reason for this is that Abs[],
Re[], Im[] etc. are not evaluated if the argument
is an expression rather than a number.

Does anyone know a way round this?


(For those interested: I am trying to calculate
the complex refractive index of a thin film from
reflectance measurements as a function of angle)

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