Questions about fitter changing

ROOT
1

Dear rooters,

could you clear my questions about fitter classes?

the core part of my program is quite simple:

...
      TH1F* counts = new TH1F("counts",
...
      TF1 *fitFcn = new TF1("fitFcn",
...
	counts->Fit("fitFcn", "MVRE");
...

Can I set default fitter before calling counts->Fit ? For example, what do I do if I want use SCAN method from MINUIT2 library (as written in FitPanel, tab “minimization”)?

At previous root versions I used (TVirtualFitter::GetFitter())->SetDefaultFitter(“Minuit2”);
but now (5.21.04) this changes nothing (as i can see from fitter output to console)

How do i change default fitter and fit routine in current root version?

I know about TMinuit, but TVirtualFitter is much more convenient for experiments with root :slight_smile:

Thanks in advance!

P.S. For running my program i use ACLiC but not interpreter mode.

2

Solution is found experimentally :bulb:
As i mentioned in my 1-st message, this code calls minuit fitter:

but when I use “+VRE” or “VRE” in “Fit” parameters it uses Minuit2 fitter.
Where am I wrong? :open_mouth:
If this is not a bug, may be you should describe this feature in details?
I hope somebody will clear this question after holidays.

3

Hi,

if you want to use Minuit2, it is enough you set before calling the Fit method

TVirtualFitter::SetDefaultFitter("Minuit2")

However, if you use the option “M”, you will force to use Minuit, since this option is not available in Minuit2.

If you find a problem, try to use the latest version, 5.22, and if you still have problems, please let me now

Best Regards

Lorenzo

4

Hello Lorenzo.
Your code also works.
The last questions in this topic:

  1. how do I change default minimization routine (for example, I’d like to try SCAN from minuit2 library)?
  2. can I change strategy for minuit/minuit2 fitters using TVirtualFitter object? if yes, how do I do this?

Thank you for your help!