rf801_mcstudy.C File Reference

Detailed Description

'VALIDATION AND MC STUDIES' RooFit tutorial macro #801

A Toy Monte Carlo study that perform cycles of

Processing /mnt/build/workspace/root-makedoc-v608/rootspi/rdoc/src/v6-08-00-patches/tutorials/roofit/rf801_mcstudy.C...

#include "RooRealVar.h"
#include "RooDataSet.h"
#include "RooGaussian.h"
#include "RooConstVar.h"
#include "RooChebychev.h"
#include "RooAddPdf.h"
#include "RooMCStudy.h"
#include "RooPlot.h"
#include "TCanvas.h"
#include "TAxis.h"
#include "TH2.h"
#include "RooFitResult.h"
#include "TStyle.h"
#include "TDirectory.h"

using namespace RooFit ;


void rf801_mcstudy()
{
   // C r e a t e   m o d e l
   // -----------------------

   // Declare observable x
   RooRealVar x("x","x",0,10) ;
   x.setBins(40) ;

   // Create two Gaussian PDFs g1(x,mean1,sigma) anf g2(x,mean2,sigma) and their parameters
   RooRealVar mean("mean","mean of gaussians",5,0,10) ;
   RooRealVar sigma1("sigma1","width of gaussians",0.5) ;
   RooRealVar sigma2("sigma2","width of gaussians",1) ;

   RooGaussian sig1("sig1","Signal component 1",x,mean,sigma1) ;
   RooGaussian sig2("sig2","Signal component 2",x,mean,sigma2) ;

   // Build Chebychev polynomial p.d.f.
   RooRealVar a0("a0","a0",0.5,0.,1.) ;
   RooRealVar a1("a1","a1",-0.2,-1,1.) ;
   RooChebychev bkg("bkg","Background",x,RooArgSet(a0,a1)) ;

   // Sum the signal components into a composite signal p.d.f.
   RooRealVar sig1frac("sig1frac","fraction of component 1 in signal",0.8,0.,1.) ;
   RooAddPdf sig("sig","Signal",RooArgList(sig1,sig2),sig1frac) ;

   // Sum the composite signal and background
   RooRealVar nbkg("nbkg","number of background events,",150,0,1000) ;
   RooRealVar nsig("nsig","number of signal events",150,0,1000) ;
   RooAddPdf  model("model","g1+g2+a",RooArgList(bkg,sig),RooArgList(nbkg,nsig)) ;



   // C r e a t e   m a n a g e r
   // ---------------------------

   // Instantiate RooMCStudy manager on model with x as observable and given choice of fit options
   //
   // The Silence() option kills all messages below the PROGRESS level, leaving only a single message
   // per sample executed, and any error message that occur during fitting
   //
   // The Extended() option has two effects:
   //    1) The extended ML term is included in the likelihood and
   //    2) A poisson fluctuation is introduced on the number of generated events
   //
   // The FitOptions() given here are passed to the fitting stage of each toy experiment.
   // If Save() is specified, the fit result of each experiment is saved by the manager
   //
   // A Binned() option is added in this example to bin the data between generation and fitting
   // to speed up the study at the expense of some precision

   RooMCStudy* mcstudy = new RooMCStudy(model,x,Binned(kTRUE),Silence(),Extended(),
                     FitOptions(Save(kTRUE),PrintEvalErrors(0))) ;


   // G e n e r a t e   a n d   f i t   e v e n t s
   // ---------------------------------------------

   // Generate and fit 1000 samples of Poisson(nExpected) events
   mcstudy->generateAndFit(1000) ;



   // E x p l o r e   r e s u l t s   o f   s t u d y
   // ------------------------------------------------

   // Make plots of the distributions of mean, the error on mean and the pull of mean
   RooPlot* frame1 = mcstudy->plotParam(mean,Bins(40)) ;
   RooPlot* frame2 = mcstudy->plotError(mean,Bins(40)) ;
   RooPlot* frame3 = mcstudy->plotPull(mean,Bins(40),FitGauss(kTRUE)) ;

   // Plot distribution of minimized likelihood
   RooPlot* frame4 = mcstudy->plotNLL(Bins(40)) ;

   // Make some histograms from the parameter dataset
   TH1* hh_cor_a0_s1f = mcstudy->fitParDataSet().createHistogram("hh",a1,YVar(sig1frac)) ;
   TH1* hh_cor_a0_a1  = mcstudy->fitParDataSet().createHistogram("hh",a0,YVar(a1)) ;

   // Access some of the saved fit results from individual toys
   TH2* corrHist000 = mcstudy->fitResult(0)->correlationHist("c000") ;
   TH2* corrHist127 = mcstudy->fitResult(127)->correlationHist("c127") ;
   TH2* corrHist953 = mcstudy->fitResult(953)->correlationHist("c953") ;



   // Draw all plots on a canvas
   gStyle->SetOptStat(0) ;
   TCanvas* c = new TCanvas("rf801_mcstudy","rf801_mcstudy",900,900) ;
   c->Divide(3,3) ;
   c->cd(1) ; gPad->SetLeftMargin(0.15) ; frame1->GetYaxis()->SetTitleOffset(1.4) ; frame1->Draw() ;
   c->cd(2) ; gPad->SetLeftMargin(0.15) ; frame2->GetYaxis()->SetTitleOffset(1.4) ; frame2->Draw() ;
   c->cd(3) ; gPad->SetLeftMargin(0.15) ; frame3->GetYaxis()->SetTitleOffset(1.4) ; frame3->Draw() ;
   c->cd(4) ; gPad->SetLeftMargin(0.15) ; frame4->GetYaxis()->SetTitleOffset(1.4) ; frame4->Draw() ;
   c->cd(5) ; gPad->SetLeftMargin(0.15) ; hh_cor_a0_s1f->GetYaxis()->SetTitleOffset(1.4) ; hh_cor_a0_s1f->Draw("box") ;
   c->cd(6) ; gPad->SetLeftMargin(0.15) ; hh_cor_a0_a1->GetYaxis()->SetTitleOffset(1.4) ; hh_cor_a0_a1->Draw("box") ;
   c->cd(7) ; gPad->SetLeftMargin(0.15) ; corrHist000->GetYaxis()->SetTitleOffset(1.4) ; corrHist000->Draw("colz") ;
   c->cd(8) ; gPad->SetLeftMargin(0.15) ; corrHist127->GetYaxis()->SetTitleOffset(1.4) ; corrHist127->Draw("colz") ;
   c->cd(9) ; gPad->SetLeftMargin(0.15) ; corrHist953->GetYaxis()->SetTitleOffset(1.4) ; corrHist953->Draw("colz") ;

   // Make RooMCStudy object available on command line after
   // macro finishes
   gDirectory->Add(mcstudy) ;
}

Author

Definition in file rf801_mcstudy.C.