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Nonliear Fit

• To: MathGroup at yoda.physics.unc.edu
• Subject: Nonliear Fit
• From: Michael Buschmann <mike at mem.unibe.ch>
• Date: Mon, 10 Jan 94 15:49:06 +0100

I'm trying to fit the magnitude of a nonlinear complex function 
of real variables to real data. I am using the NonlinearFit routine
in the Statistics standard package directory (John Novak Feb 1992)
When I am able to find an real analytic expression for the magnitude
of the complex function, the routine works fine. When I simply place
The Abs[] operator around the complex function, no fitting is 
done and the initial values are returned. When I use an interpolation
function to represent the magnitude of the complex function I get
a 'dmval' error message that the input value lies outside the domain
of the interpolation function, even though it does not. I would like to
get the fit working without having to always find an analytic expression
for the magnitude of the complex function. Either using the Abs[]
operator or an interpolation. Any ideas ?

Mike Buschmann