%%cpp -d
#include "RooRealVar.h"
#include "RooDataSet.h"
#include "RooPolyVar.h"
#include "TCanvas.h"
#include "TAxis.h"
#include "RooPlot.h"
#include "TRandom.h"

using namespace RooFit;

RooRealVar x("x", "x", -11, 11);
RooRealVar y("y", "y", -10, 200);
RooDataSet dxy("dxy", "dxy", {x, y}, StoreError({x, y}));

for (int i = 0; i <= 10; i++) {

   // Set X value and error
   x = -10 + 2 * i;
   x.setError(i < 5 ? 0.5 / 1. : 1.0 / 1.);

   // Set Y value and error
   y = x.getVal() * x.getVal() + 4 * fabs(gRandom->Gaus());
   y.setError(sqrt(y.getVal()));

   dxy.add({x, y});
}

RooRealVar a("a", "a", 0.0, -10, 10);
RooRealVar b("b", "b", 0.0, -100, 100);
RooRealVar c("c", "c", 0.0, -100, 100);
RooPolyVar f("f", "f", x, RooArgList(b, a, c));

RooPlot *frame = x.frame(Title("Chi^2 fit of function set of (X#pmdX,Y#pmdY) values"));
dxy.plotOnXY(frame, YVar(y));

std::unique_ptr<RooFitResult> fit1{f.chi2FitTo(dxy, YVar(y), Save(), PrintLevel(-1))};
fit1->Print();

f.plotOn(frame);

std::unique_ptr<RooFitResult> fit2{f.chi2FitTo(dxy, YVar(y), Save(), PrintLevel(-1), Integrate(true))};
fit2->Print();

f.plotOn(frame, LineStyle(kDashed), LineColor(kRed));

new TCanvas("rf609_xychi2fit", "rf609_xychi2fit", 600, 600);
gPad->SetLeftMargin(0.15);
frame->GetYaxis()->SetTitleOffset(1.4);
frame->Draw();

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