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Reference Guide
rf501_simultaneouspdf.C File Reference

Detailed Description

View in nbviewer Open in SWAN 'ORGANIZATION AND SIMULTANEOUS FITS' RooFit tutorial macro #501

Using simultaneous p.d.f.s to describe simultaneous fits to multiple datasets



Processing /mnt/build/workspace/root-makedoc-v608/rootspi/rdoc/src/v6-08-00-patches/tutorials/roofit/rf501_simultaneouspdf.C...
#include "RooRealVar.h"
#include "RooDataSet.h"
#include "RooGaussian.h"
#include "RooConstVar.h"
#include "RooChebychev.h"
#include "RooAddPdf.h"
#include "RooCategory.h"
#include "TCanvas.h"
#include "TAxis.h"
#include "RooPlot.h"
using namespace RooFit ;
void rf501_simultaneouspdf()
{
// C r e a t e m o d e l f o r p h y s i c s s a m p l e
// -------------------------------------------------------------
// Create observables
RooRealVar x("x","x",-8,8) ;
// Construct signal pdf
RooRealVar mean("mean","mean",0,-8,8) ;
RooRealVar sigma("sigma","sigma",0.3,0.1,10) ;
RooGaussian gx("gx","gx",x,mean,sigma) ;
// Construct background pdf
RooRealVar a0("a0","a0",-0.1,-1,1) ;
RooRealVar a1("a1","a1",0.004,-1,1) ;
RooChebychev px("px","px",x,RooArgSet(a0,a1)) ;
// Construct composite pdf
RooRealVar f("f","f",0.2,0.,1.) ;
RooAddPdf model("model","model",RooArgList(gx,px),f) ;
// C r e a t e m o d e l f o r c o n t r o l s a m p l e
// --------------------------------------------------------------
// Construct signal pdf.
// NOTE that sigma is shared with the signal sample model
RooRealVar mean_ctl("mean_ctl","mean_ctl",-3,-8,8) ;
RooGaussian gx_ctl("gx_ctl","gx_ctl",x,mean_ctl,sigma) ;
// Construct the background pdf
RooRealVar a0_ctl("a0_ctl","a0_ctl",-0.1,-1,1) ;
RooRealVar a1_ctl("a1_ctl","a1_ctl",0.5,-0.1,1) ;
RooChebychev px_ctl("px_ctl","px_ctl",x,RooArgSet(a0_ctl,a1_ctl)) ;
// Construct the composite model
RooRealVar f_ctl("f_ctl","f_ctl",0.5,0.,1.) ;
RooAddPdf model_ctl("model_ctl","model_ctl",RooArgList(gx_ctl,px_ctl),f_ctl) ;
// G e n e r a t e e v e n t s f o r b o t h s a m p l e s
// ---------------------------------------------------------------
// Generate 1000 events in x and y from model
RooDataSet *data = model.generate(RooArgSet(x),100) ;
RooDataSet *data_ctl = model_ctl.generate(RooArgSet(x),2000) ;
// C r e a t e i n d e x c a t e g o r y a n d j o i n s a m p l e s
// ---------------------------------------------------------------------------
// Define category to distinguish physics and control samples events
RooCategory sample("sample","sample") ;
sample.defineType("physics") ;
sample.defineType("control") ;
// Construct combined dataset in (x,sample)
RooDataSet combData("combData","combined data",x,Index(sample),Import("physics",*data),Import("control",*data_ctl)) ;
// C o n s t r u c t a s i m u l t a n e o u s p d f i n ( x , s a m p l e )
// -----------------------------------------------------------------------------------
// Construct a simultaneous pdf using category sample as index
RooSimultaneous simPdf("simPdf","simultaneous pdf",sample) ;
// Associate model with the physics state and model_ctl with the control state
simPdf.addPdf(model,"physics") ;
simPdf.addPdf(model_ctl,"control") ;
// P e r f o r m a s i m u l t a n e o u s f i t
// ---------------------------------------------------
// Perform simultaneous fit of model to data and model_ctl to data_ctl
simPdf.fitTo(combData) ;
// P l o t m o d e l s l i c e s o n d a t a s l i c e s
// ----------------------------------------------------------------
// Make a frame for the physics sample
RooPlot* frame1 = x.frame(Bins(30),Title("Physics sample")) ;
// Plot all data tagged as physics sample
combData.plotOn(frame1,Cut("sample==sample::physics")) ;
// Plot "physics" slice of simultaneous pdf.
// NBL You _must_ project the sample index category with data using ProjWData
// as a RooSimultaneous makes no prediction on the shape in the index category
// and can thus not be integrated
simPdf.plotOn(frame1,Slice(sample,"physics"),ProjWData(sample,combData)) ;
simPdf.plotOn(frame1,Slice(sample,"physics"),Components("px"),ProjWData(sample,combData),LineStyle(kDashed)) ;
// The same plot for the control sample slice
RooPlot* frame2 = x.frame(Bins(30),Title("Control sample")) ;
combData.plotOn(frame2,Cut("sample==sample::control")) ;
simPdf.plotOn(frame2,Slice(sample,"control"),ProjWData(sample,combData)) ;
simPdf.plotOn(frame2,Slice(sample,"control"),Components("px_ctl"),ProjWData(sample,combData),LineStyle(kDashed)) ;
TCanvas* c = new TCanvas("rf501_simultaneouspdf","rf403_simultaneouspdf",800,400) ;
c->Divide(2) ;
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() ;
}
Author
07/2008 - Wouter Verkerke

Definition in file rf501_simultaneouspdf.C.