# Fittings slices of a 2-d histogram

    {
    //
    // To see the output of this macro, click  here
    //    This macro illustrates how to use the TH1::FitSlicesY function
    //    It uses the TH2F histogram generated in macro hsimple.C
    //    It invokes FitSlicesY and draw the fitted "mean" and "sigma"
    //    in 2 sepate pads.
    //    This macro shows also how to annotate a picture, change
    //    some pad parameters.
    //
       gROOT->Reset();

    // Change some default parameters in the current style
       gStyle->SetLabelSize(0.06,"x");
       gStyle->SetLabelSize(0.06,"y");
       gStyle->SetFrameFillColor(38);
       gStyle->SetTitleW(0.6);
       gStyle->SetTitleH(0.1);

    // Connect the input file and get the 2-d histogram in memory
       TFile *hsimple = new TFile("hsimple.root");
       TH2F *hpxpy = (TH2F*)hsimple->Get("hpxpy");

    // Create a canvas and divide it
       TCanvas *c1 = new TCanvas("c1","c1",700,500);
       c1->SetFillColor(42);
       c1->Divide(2,1);
       c1->cd(1);
       TPad *left = (TPad*)gPad;
       left->Divide(1,2);

    // Draw 2-d original histogram
       left->cd(1);
       gPad->SetTopMargin(0.12);
       gPad->SetFillColor(33);
       hpxpy->Draw();
       hpxpy->GetXaxis()->SetLabelSize(0.06);
       hpxpy->GetYaxis()->SetLabelSize(0.06);
       hpxpy->SetMarkerColor(kYellow);

    // Fit slices projected along Y fron bins in X [7,32]
       hpxpy->FitSlicesY(0,0,0,20);

    // Show fitted "mean" for each slice
       left->cd(2);
       gPad->SetFillColor(33);
       hpxpy_0->Draw();
       c1->cd(2);
       TPad *right = (TPad*)gPad;
       right->Divide(1,2);
       right->cd(1);
       gPad->SetTopMargin(0.12);
       gPad->SetLeftMargin(0.15);
       gPad->SetFillColor(33);
       hpxpy_1->Draw();

    // Show fitted "sigma" for each slice
       right->cd(2);
       gPad->SetTopMargin(0.12);
       gPad->SetLeftMargin(0.15);
       gPad->SetFillColor(33);
       hpxpy_2->SetMinimum(0.8);
       hpxpy_2->Draw();

    //attributes
       hpxpy_0->SetLineColor(kYellow);
       hpxpy_1->SetLineColor(kYellow);
       hpxpy_2->SetLineColor(kYellow);
       hpxpy_0->SetMarkerColor(kRed);
       hpxpy_1->SetMarkerColor(kRed);
       hpxpy_2->SetMarkerColor(kRed);
       hpxpy_0->SetMarkerStyle(21);
       hpxpy_1->SetMarkerStyle(21);
       hpxpy_2->SetMarkerStyle(21);
       hpxpy_0->SetMarkerSize(0.6);
       hpxpy_1->SetMarkerSize(0.6);
       hpxpy_2->SetMarkerSize(0.6);
    }