using namespace RooFit;

RooWorkspace w("w");

w.factory("NonCentralChiSquare::nc(x[0,50],k[1.99,0,5],lambda[5])");

w.factory("NonCentralChiSquare::ncc(x,kk[2.01,0,5],lambda)");

w.factory("NonCentralChiSquare::nccc(x,kk,lambda)");
((RooNonCentralChiSquare *)w.pdf("nccc"))->SetForceSum(true);

w.factory("ChiSquarePdf::cs(x,k)");

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();

%jsroot on
gROOT->GetListOfCanvases()->Draw()