TestNonCentral.C

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/// \file
/// \ingroup tutorial_roostats
/// \notebook -js
/// Demonstrates non central chi-square.
///
/// \macro_image
/// \macro_output
/// \macro_code
///
/// \author Lorenzo Moneta
 
using namespace RooFit;
void TestNonCentral()
{
 
   RooWorkspace w("w");
   // k <2, must use sum
   w.factory("NonCentralChiSquare::nc(x[0,50],k[1.99,0,5],lambda[5])");
   // kk > 2 can use bessel
   w.factory("NonCentralChiSquare::ncc(x,kk[2.01,0,5],lambda)");
   // kk > 2, force sum
   w.factory("NonCentralChiSquare::nccc(x,kk,lambda)");
   ((RooNonCentralChiSquare *)w.pdf("nccc"))->SetForceSum(true);
 
   // a normal "central" chi-square for comparison when lambda->0
   w.factory("ChiSquarePdf::cs(x,k)");
 
   // w.var("kk")->setVal(4.); // test a large kk
 
   std::unique_ptr<RooDataSet> ncdata{w.pdf("nc")->generate(*w.var("x"), 100)};
   std::unique_ptr<RooDataSet> csdata{w.pdf("cs")->generate(*w.var("x"), 100)};
   RooPlot *plot = w.var("x")->frame();
   ncdata->plotOn(plot, MarkerColor(kRed));
   csdata->plotOn(plot, MarkerColor(kBlue));
   w.pdf("nc")->plotOn(plot, LineColor(kRed));
   w.pdf("ncc")->plotOn(plot, LineColor(kGreen));
   w.pdf("nccc")->plotOn(plot, LineColor(kYellow), LineStyle(kDashed));
   w.pdf("cs")->plotOn(plot, LineColor(kBlue), LineStyle(kDotted));
   plot->Draw();
}