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J
jcoolman1-Visitor
1-Visitor
November 24, 2020
Solved

genfit problem about number of parameters

  • November 24, 2020
  • 1 reply
  • 2796 views

The error message says the number of fitting parameters and guess values must be the same, but they do !!!

Please, take a look to the file attached, this is a short programm.

Best answer by Werner_E

Not exactly sure what you mean by "The combination of these three functions gives a family of non-asymptotic sigmoid functions". Which kind of "combination"?

If you have a simple additive combination in mind, you would have to do it that way, nut the result sure is not satisfactory (and very sensitive wrt the guess values):

Werner_E_0-1606247813739.png

But if you want to say that you would like to split your curve into three parts and fit a different function type to each part, then you would have to do the splitting yourself and fit three times.

 

BTW, Here's a function which seems to fit your data pretty well:

Werner_E_1-1606248764584.png

 

 

 

1 reply

W
Werner_E25-Diamond IAnswer
25-Diamond I
November 24, 2020

Not exactly sure what you mean by "The combination of these three functions gives a family of non-asymptotic sigmoid functions". Which kind of "combination"?

If you have a simple additive combination in mind, you would have to do it that way, nut the result sure is not satisfactory (and very sensitive wrt the guess values):

Werner_E_0-1606247813739.png

But if you want to say that you would like to split your curve into three parts and fit a different function type to each part, then you would have to do the splitting yourself and fit three times.

 

BTW, Here's a function which seems to fit your data pretty well:

Werner_E_1-1606248764584.png

 

 

 
J
jcoolman1-VisitorAuthor
1-Visitor
November 25, 2020

Yeah, I was talking about "linear combinations of functions" , sorry.

Thanks, you helped me to fix this error, now I can fit with genfit.

I think mathcad is not good for fitting points if they are not well close to a mathematical curve, but experimental points are random up and down from such a curve.

I was hopping to fit experimental points to non asymptotic sigmoid curves like this https://stats.stackexchange.com/questions/398551/logistic-function-with-a-slope-but-no-asymptotes

(because some chemical law predicts this) you see there are 5 paramenters, I also added a sixth parameter x0  in this form: instead x I put (x-x0) hopping the fitting process could find the best x0, but the outcome was ugly.

SigmaPlot can fit this without problem (sorry for comparison) but at the moment I haven't this software.

Thank you anyway.

W
Werner_E25-Diamond I
25-Diamond I
November 25, 2020

Mathcad often is very sensible with respect to the guess values which will have to be chosen with great care.

You may want to have a look at the eval version of CurveExpert Pro. Even in demo w/o the various export options mode its quite useful for curve fitting. It has a lot of predefined function types which it tries on the data and you may also define your own.

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