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Nonlinear fit for a non-differentiable function

  • To: mathgroup at smc.vnet.net
  • Subject: [mg43119] Nonlinear fit for a non-differentiable function
  • From: Ahmed Sayeed <Ahmed.Sayeed at Tu-Ilmenau.De>
  • Date: Wed, 13 Aug 2003 07:49:51 -0400 (EDT)
  • Reply-to: Ahmed Sayeed <Ahmed.Sayeed at Tu-Ilmenau.De>
  • Sender: owner-wri-mathgroup at wolfram.com

Hello friends,
   I have to carry out a nonlinear fit where the fit function is non-differentiable w.r.t. one or
more of the parameters, because I have to take the absolute value in the definition of the function.
For example, f[x_,a_,b_]:=a*Sin[Abs[b]*x], where a and b are fit parameters.  NonlinearRegress
fails, giving the following message:
NonlinearRegress::"unevldr": "One or more derivatives of the model with \
respect to parameters did not evaluate."
   I shall be grateful if someone could suggest a way around this problem. 
                               Thanks
                               Sayeed 


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