Linear fit

[booghimen]

Hi rooters!!
I have a problem, maybe a stupid problem, with a linear fit, in fact if I fit my graph with a predefinite linear fit “pol1” I obtain this result:

instead if I use a user function: f1 = TF1 (“f1”, " [0]+[1]*x" ) I obtain this other result:

Why this?

thanks for the help!!

[Pepe_Le_Pew]

Before trying to do fit using your own functions, did you set “initial values” for function parameters?
You should have something like this: TF1 *f1 = new TF1("f1", "[0]+[1]*x", 2900, 6100); // "xmin" and "xmax" are required f1->SetParameters(0, 0.001);

[booghimen]

Yes is due for this reason!!! thanks a lot!!!
Now I have another problem…
From the fit I take the 1st parameters, and until here is ok:

p0= f2->GetParameter(0)
p1= f2->GetParameter(1)

but then I have to use this parameter to draw a line, so I tried to do:

TF1 f3= new TF1 (“f3”, "p0+(2p1*x)", 0,12000)

but don’t work.
thanks for the help!!

[Pepe_Le_Pew]

TF1 *f3 = new TF1("f3", "[0]+2.0*[1]*x", 0, 12000); f3->SetTitle("p0+(2*p1*x);HV_{eff}^{} [kV];Density Current [#muA/cm^{2}_{}]"); f3->SetParameters(p0, p1); or: TF1 *f3 = new TF1("f3", "pol1", 0, 12000); f3->SetParameters(p0, 2.0*p1);

[booghimen]

Perfect!! now work very well!!!
The last question is about the statistic box:

1. I have to set the statistic box of 2 graph, so I want put the 2 box in different position, so I tried to do this for 1st plot :

gStyle.SetOptFit(1111)
gStyle.SetStatX(0.35)
gStyle.SetStatY(0.7)
gStyle.SetStatH(0.25)
gStyle.SetStatW(0.1)

Then the same command with different values for the 2nd plot, but I obtain the 2 box in the same place. How can I do?

2. I know how the H and W of statistic box, but I didn’t found how set the label of the box. How can I do to set it?

Thanks a lot =) =)

[Pepe_Le_Pew]

Print in Graph Legend fit parameters

[code]# include “TCanvas.h” include “TROOT.h” include “TStyle.h” include “TMultiGraph.h” include “TGraphErrors.h” include “TF1.h” include “TLegend.h” include “TPaveStats.h” include “TArrow.h” include “TLatex.h” void gain(){ TCanvas *mycanvas = new TCanvas(“c”,“c”,600, 400); TMultiGraph * mg = new TMultiGraph(“gain curve”,“GAIN CURVE”); // The values on the X,Y axes and error on Y axis const int n_Fe=20; double x_Fe[n_Fe]={560,565,570,575,580,585,590,595,600,605,610,615,620,625,630,635,640,…

How to move statistics box when using Draw("sames"

// http://root.cern.ch/root/html/TStyle.html#TStyle:SetOptStat gStyle->SetOptStat(1111); // ... // http://root.cern.ch/root/html/TH1.html#TH1:SetStats // SomeHisto->SetStats(kTRUE); // ... // http://root.cern.ch/root/html/THistPainter.html SomeHisto->Draw("SAMES"); // you MUST draw "SomeHisto" first (e.g. with "SAMES") gPad->Modified(); gPad->Update(); // make sure it's really (re)drawn // http://root.cern.ch/root/html/TPaveStats.html #if 1 /* 0 or 1 */ TPaveStats *s = ((TPaveStats*)(SomeHisto->F…

TH2 Custom Stats?

Note “h->SetStats(kFALSE); // mandatory (not sure why)”: [code]{ gStyle->SetOptStat(); // mandatory TCanvas *c = new TCanvas(“c”, “c”, 600, 400); TH2F h = new TH2F(“h”, "TH2F example ", 30, -4, 4, 30, -20, 20); Float_t px, py; for (Int_t i = 0; i < 25000; i++) { gRandom->Rannor(px, py); h->Fill(px-1, 5py); h->Fill(2+0.5px, 2py-10., 0.1); } h->SetStats(kTRUE); h->Draw(“COLZ”); gPad->Modified(); gPad->Update(); // mandatory TPaveStats ps = (TPaveStats)gPad->GetPrimitive(“stats”); if …

Adding fit parameters into statistical box

[code] gStyle->SetOptFit(1); h_ccd_CTE_L->SetOption(“p”); TF1 *pol1_LCCD = new TF1(“pol1”,“pol1”,lower_x_hist_cte,upper_x_hist_cte); h_ccd_CTE_L->Fit(pol1_LCCD,“R”); gPad->Modified(); gPad->Update(); // make sure it’s (re)drawn // https://root.cern.ch/root/html/TPaveStats.html TPaveStats st = (TPaveStats)h_ccd_CTE_L->FindObject(“stats”); st->SetX1NDC(0.7); st->SetX2NDC(0.99); st->SetY1NDC(0.2); st->SetY2NDC(0.5); st->SetName(“mystats”); h_ccd_CTE_L->SetStats(0); TList *list = st->G…

[booghimen]

Very good, but now I obtain a double statistic box, 1 created with Tpave, and 1 by gStyle…
so I put 0 the option of gStyle :

gStyle.SetOptFit()
gStyle.SetStatX(0)
gStyle.SetStatY(0)
gStyle.SetStatH(0)
gStyle.SetStatW(0)

And in this way don’t appear.
I know that for the histo there is a command to hide the statistic box, like:
hist->SetStat(0)

for graph there is not a command like this?

[Pepe_Le_Pew]

You should have: gStyle->SetOptFit(0);
If this doesn’t help, try to delete it (after it is drawn).
In worst case you can always move it to “out of the frame”.