gr003_errors2.C

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/// \file
/// \ingroup tutorial_graphs
/// \notebook -js
/// \preview Create and draw two graphs with error bars, superposed on the same canvas
///
/// We first draw an empty frame with the axes, then draw the graphs on top of it
/// Note that the graphs should have the same or very close ranges (in both axis),
/// otherwise they may not be visible in the frame.
///
/// Alternatively, an automatic axis scaling can be achieved via a
/// [TMultiGraph](https://root.cern/doc/master/classTMultiGraph.html)
///
/// See the [TGraphErrors documentation](https://root.cern/doc/master/classTGraphErrors.html)
///
/// \macro_image
/// \macro_code
/// \author Rene Brun
 
void gr003_errors2() {
   TCanvas *c1 = new TCanvas("c1","2 graphs with errors",200,10,700,500);
   c1->SetGrid();
 
   // draw a frame to define the range
   TH1F *hr = c1->DrawFrame(-0.4,0,1.2,12);
   hr->SetXTitle("X title");
   hr->SetYTitle("Y title");
   c1->GetFrame()->SetBorderSize(12);
 
   // create first graph
   // We will use the constructor requiring: the number of points, arrays containing the x-and y-axis values, and arrays with the x- andy-axis errors
   const Int_t n1 = 10;
   Double_t xval1[]  = {-0.22, 0.05, 0.25, 0.35, 0.5, 0.61,0.7,0.85,0.89,0.95};
   Double_t yval1[]  = {1,2.9,5.6,7.4,9,9.6,8.7,6.3,4.5,1};
   Double_t ex1[] = {.05,.1,.07,.07,.04,.05,.06,.07,.08,.05};
   Double_t ey1[] = {.8,.7,.6,.5,.4,.4,.5,.6,.7,.8};
   // If all x-axis errors should zero, just provide a single 0 in place of ex1
   TGraphErrors *gr1 = new TGraphErrors(n1,xval1,yval1,ex1,ey1);
   gr1->SetMarkerColor(kBlue);
   gr1->SetMarkerStyle(21);
   // Since we already have a frame in the canvas, we draw the graph without the option "A" (which draws axes for this graph)
   gr1->Draw("LP");
 
   // create second graph
   const Int_t n2 = 10;
   Float_t xval2[]  = {-0.28, 0.005, 0.19, 0.29, 0.45, 0.56,0.65,0.80,0.90,1.01};
   Float_t yval2[]  = {0.82,3.86,7,9,10,10.55,9.64,7.26,5.42,2};
   Float_t ex2[] = {.04,.12,.08,.06,.05,.04,.07,.06,.08,.04};
   Float_t ey2[] = {.6,.8,.7,.4,.3,.3,.4,.5,.6,.7};
   TGraphErrors *gr2 = new TGraphErrors(n2,xval2,yval2,ex2,ey2);
   gr2->SetMarkerColor(kRed);
   gr2->SetMarkerStyle(20);
   gr2->Draw("LP");
}