ROOT.gStyle.SetOptFit(1111)

Newbie
3

Thanks for your answer and suggestions.
I’m still getting the same values.
Do you have an other idea what I could try?
Thanks again and cheers!

4

Do you have a small reproducer?

5

A possible source could be mixing “double”/“Double_t” and “float”/“Float_t” variables.

6

Hi again,

here is a short overview on the code:

ROOT.gStyle.SetOptTitle(0);
ROOT.gStyle.SetOptStat(0);
ROOT.gStyle.SetOptFit(1111);
ROOT.gStyle.SetStatBorderSize(0);

Datareadin=float(data[j])
mc = ROOT.TCanvas(“fit”, “fit”, 1024, 200, 700, 500)
graph = ROOT.TGraphErrors(n, ff, sig, ROOT.nullptr, sigErr)
rfitfunc = ROOT.TF1(“rfit”, fitfunc, min, max, npars)
/set fit parameter etc
fitresults = graph.Fit(rfitfunc, “QERMBS”)
/save fit results in file via fitresults.Parameter()
graph.Draw(“APE”)
mc.Update()

ps = mc.GetPrimitive(“stats”)
ps.SetFitFormat(“5.15f”)
ps.SetStatFormat(“6.4f”)
mc.Modified()
mc.Update()

Saved fit results are not the same as the one shown in the canvas.

7

So, what exactly do you get “in the canvas” versus “saved in a file” (e.g., do you get 15 decimal digits precision in both cases?).

8

I get i.e. 1.4301894903 (canvas with ps.SetFitFormat(“5.11g”)) and 1.4301894936 in the file.
And I’m using also an optimizer (ROOT.Math.MinimizerOptions.SetDefaultPrecision(1e-18)) in case that’s important.

9

@couet It seems there is a bug in TPaveStats … it internally converts the original “double”/“Double_t” values into “float”/“Float_t” (which are then displayed).

Try: ((float)1.4301894936) - 1.4301894903f

10

@Wile_E_Coyote @L_N : do you have a reproducer showing the problem?

11

Just “gStyle->SetFitFormat("5.17g");”, fit anything, and then:
printf("%5.17g %5.17g\n", f->GetParameter(0), ((float)f->GetParameter(0)));

12

I made this:

Double_t fitf(Double_t *x, Double_t *par)
{
   return x[0]*x[0]*par[0]+x[0]*par[1];
}

void L_N()
{
   gStyle->SetOptFit(1111) ;

   const Int_t n = 4;
   Double_t x[n]= {0.3156, 1.0012, 1.4146, 8.4996};
   Double_t y[n]= {1.881, 5.899, 8.376, 50.239};

   auto gr = new TGraph(n,x,y);
   gr->Draw("A*");

   TF1 *f = new TF1("f", fitf,0, 9, 2);
   f->SetParameters(-0.01, 5.9);
   gr->Fit(f);
   printf("%5.17g %5.17g\n", f->GetParameter(0), ((float)f->GetParameter(0)));

}

Screenshot 2023-03-17 at 14.32.17
Screenshot 2023-03-17 at 14.32.17816×440 43.5 KB 

****************************************
Minimizer is Minuit / Migrad
Chi2                      =  0.000799383
NDf                       =            2
Edm                       =  3.07171e-24
NCalls                    =           36
p0                        = -0.000278198   +/-   0.00159679  
p1                        =      5.91312   +/-   0.0132961   
-0.00027819773415341253 -0.00027819772367365658

Does it reproduce what you are complaining about?

13

@couet Add: gStyle->SetFitFormat("5.17g");

14

Thanks a lot for your efforts.
Yes, could you please add SetFitFormat(“5.17g”) to check if you values also deviate?

15

it seems so:

Screenshot 2023-03-17 at 14.53.03
Screenshot 2023-03-17 at 14.53.03998×652 74.4 KB

16

If I remove the float casting I get:

Screenshot 2023-03-17 at 15.01.10
Screenshot 2023-03-17 at 15.01.101020×660 77.2 KB

17

Ok, what does that mean now exactly, so I guess f->GetParameter(0) is wrong and the float casting is needed?

18

is the 2nd output right ?

19

Please let me know what you think and how to proceed. Are the values extracted via f->GetParameter not trustworthy?

20

Yes they are

21

Sorry, I meant (float)f->GetParameter are trustworthy and f->GetParameter are not?

22

f->GetParameter is fine, it returns s double.