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Thibault

About fit precison and reproductibility

Asked by Thibault
on 19 Jul 2013

Hi everyone, I'm using the Curve Fitting toolbox to analyse some data. I recently observed that I get very different results if I use the suggested Exponential fit or if I manually enter my expression in 'Custom equation' mode. Maybe It is not surprising that the custom equation mode is a little less powerful than the 'specialized' ones, but I wanted it confirmed.

Another question is : 'How can constraint some of the fit parameters so I can reduce degrees of liberty' ?

Thank you

  1 Comment

dpb
on 19 Jul 2013

Need precise description of what you did the two ways that you think are more different than what you expected. I've got the curve fitting toolbox but haven't yet had time to explore with it. But I'd certainly think if you enter the same model manually as the auto one and use consistent data and fitting techniques the results should be essentially the same.

IOW I think you've done something different to cause the difference whether you recognize what that something is or not.

You can apparently (as I read the documentation, anyway) add constraints on any of the parameters of the chosen model in the options dialog. I see it also says it only uses the constrains with the trust region fitting algorithm.

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