[ROOT] fitting gaussian+landau

From: Tahsina Ferdousi (tahsina@ucrhi2.ucr.edu)
Date: Wed Dec 12 2001 - 22:07:13 MET


Hi Rooters,

I was trying to fit a histogram with a gaussian+landau. My intention was
as follows. The histogram ranges from -20 to 200. I want to fit the range
from -20 to 10 with a gaussian and from 10 to 200 with a landau. Then I
add the two fitting functions (gaus+landau) to fit the overall
distribution. Here comes my problem I want the overall fit (which from now
on we call "total") to follow a gaussian shape between -20 and 10 and then
a landau shape between 10 and 200. But instead what I get is a continuous
fitting shape (with no dip at 10 and no bump at 15, where the MPV of the
landau is). I was following the "How to fit in a sub-range of an
histogram" from the ROOT tutorial.

I would appreciate if someone could kindly point me where I am doing wrong
(or should I try some other procedure as $ROOTSYS/tutorials/FittingDemo.C
where I define my own function).

I am attaching the code I used (which is
really $ROOTSYS/tutorials/multifit.C)

//*************************
   TFile *f = new TFile("ADC_final.root");
   adc_high_cent4 = (TH1F*)f->Get("adc_high_cent4");

   g2 = new TF1("g2","landau",10,200);
   g1 = new TF1("g1","gaus",-20,10);
   total = new TF1("total","landau(0)+gaus(0)",-20,200);
   total->SetLineColor(2);
   g1->SetLineColor(4);
   adc_high_cent4->Fit("g1","R0");
   g1->GetParameters(&par[0]);
   adc_high_cent4->Fit("g2","R0+");
   g2->GetParameters(&par[3]);
   total->SetParameters(par);
   adc_high_cent4->Fit("total","R0+");
   adc_high_cent4->Draw();
   g1->Draw("same");
   g2->Draw("same");
   total->Draw("same");
//*************************

Best Regards,

-tahsina

-----------------------------------------------------------------------------
                                Tahsina Ferdousi
------------------------------------------------------------------------------
Graduate Student         |email:                     |Phone:
Department of Physics    |tahsina@phyun0.ucr.edu     |(909)-787-7301
University of California |tahsina@ucrhi2.ucr.edu     |
Riverside, CA 92521      |url:                       |
USA                      |www.phenix.bnl.gov/~tahsina|
------------------------------------------------------------------------------



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