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Nonlinear curve-fitting difficult functions

  • To: mathgroup at
  • Subject: [mg6579] Nonlinear curve-fitting difficult functions
  • From: Jeff Hammock <hammockj at>
  • Date: Fri, 4 Apr 1997 02:11:31 -0500 (EST)
  • Organization: The University of Alabama in Huntsville
  • Sender: owner-wri-mathgroup at


I frequently use the MMA package Statistics`NonlinearFit` to perform
fits to data using equations such as:

	f[x_,y_,]:= x Sin[y] 

The package uses the Levenberg-Marquardt method to itteratively find the
best-fit solution.  This works fine if I have a nice closed-form
solution with well-behaved derivatives.

I WANT to be able to use model functions like:

	f[x_,y_]:= NIntegrate[g[x,i],{i,0,y}]

or ANY other function that I can generate that does not have a
closed-form solution.

Does anyone know a trick to force the existing MMA package into using
numerically calculated derivatives in its optimization?

Or, has anyone written a nonlinear fitting routine that handles this
type of functions?

Thanks in advance for any insights....


Matthew Smith, Ph.D.
Research Scientist
The University of Alabama in Huntsville

smithmh at

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