TF1 Parameters in Fit

ROOT
1

Hello Rooters,

I have the following question:

Is is possible to fix the parameters of a TF1 function
such that e.g. for a pol1 fit I do something like

TF1 *f = new TF1(“f”,"[0]+[1]*x",0,1);
f->SetParameter(1,8000); // and
f->SetParError(1,400);
histo->Fit(f);

and have the parameter fixed within this range for the fit, such that the outcome for [0] would include the given error on [1] ?

The above code does not lead to the desired result,

Also using SetParLimits does not work, having
f->SetParLimits(1,7600,8400);
does always end up with 8400 being used for the fit, and the error being calculated again.

I would be glad for any suggestions on this subject.

Cheers

Erik

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2

The right method is to use:

f->SetParLimits(1,min,max);

if fit converge to the limits problably there some other problems, in example data don’t follow the simple linear relation.