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MathGroup Archive 2007

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errors of NonlinearRegress

  • To: mathgroup at smc.vnet.net
  • Subject: [mg75122] errors of NonlinearRegress
  • From: Fulya "Bac" <fulya_bagci at yahoo.com>
  • Date: Wed, 18 Apr 2007 04:55:12 -0400 (EDT)

Hello everyone,
   
  I want to fit data to a function and find two parameters beta and beam radius. I gave them starting, minimum and maximum values. But NonlinearRegress always iteres the same from 26 to 40. iterations and it does not itere after iteration 40. It does not even find  beta and beam radius when I put PrecisionGoal. The fitted parameter values are not correct. Why? What do I have to do?.
   
  Here are the errors:
  The step size in the search has become less than the tolerance prescribed by the PrecisionGoal option, but the gradient is larger than the tolerance specified by the AccuracyGoal option. There is a possibility that the method has stalled at a point which is not a local minimum.
  NonlinearRegress was unable to compute a design matrix, because it couldn't find derivatives of the model. Some requested diagnostics may not be able to be generated.
   
  I would be very grateful if somebody could help me on this problem
Many thanks. 
   
  Best regards,
   
  Fulya



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