1 // Builds a graph with errors, displays it and saves it
   2 // as image. First, include some header files (within,
   3 // CINT these will be ignored).
   4 
   5 #include "TCanvas.h"
   6 #include "TROOT.h"
   7 #include "TGraphErrors.h"
   8 #include "TF1.h"
   9 #include "TLegend.h"
  10 #include "TArrow.h"
  11 #include "TLatex.h"
  12 
  13 void MyMacro(){
  14   // The values and the errors on the Y axis
  15   const int n_points=10;
  16     double x_vals[n_points]=
  17       {1,2,3,4,5,6,7,8,9,10};
  18     double y_vals[n_points]=
  19       {6,12,14,20,22,24,35,45,44,53};
  20     double y_errs[n_points]=
  21       {5,5,4.7,4.5,4.2,5.1,2.9,4.1,4.8,5.43};
  22 
  23     // Instance of the graph
  24     TGraphErrors graph(n_points,x_vals,y_vals,NULL,y_errs);
  25     graph.SetTitle("Measurement XYZ;lenght [cm];Arb.Units");
  26 
  27     // Make the plot looks better
  28     graph.SetMarkerStyle(kOpenCircle);
  29     graph.SetMarkerColor(kBlue);
  30     graph.SetLineColor(kBlue);
  31 
  32     // The canvas on which we'll draw the graph
  33     TCanvas* mycanvas = new TCanvas();
  34 
  35     // Draw the graph !
  36     graph.DrawClone("APE");
  37 
  38     // Define a linear function
  39     TF1 f("Linear law","[0]+x*[1]",.5,10.5);
  40     // Let's make the function line nicer
  41     f.SetLineColor(kRed); f.SetLineStyle(2);
  42     // Fit it to the graph and draw it
  43     graph.Fit(&f);
  44     f.DrawClone("Same");
  45 
  46     // Build and Draw a legend
  47     TLegend leg(.1,.7,.3,.9,"Lab. Lesson 1");
  48     leg.SetFillColor(0);
  49     graph.SetFillColor(0);
  50     leg.AddEntry(&graph,"Exp. Points");
  51     leg.AddEntry(&f,"Th. Law");
  52     leg.DrawClone("Same");
  53 
  54     // Draw an arrow on the canvas
  55     TArrow arrow(8,8,6.2,23,0.02,"|>");
  56     arrow.SetLineWidth(2);
  57     arrow.DrawClone();
  58 
  59     // Add some text to the plot
  60     TLatex text(8.2,7.5,"#splitline{Maximum}{Deviation}");
  61     text.DrawClone();
  62 
  63     mycanvas->Print("graph_with_law.pdf");
  64 }
  65 
  66 #ifndef __CINT__
  67 int main(){
  68   MyMacro();
  69 }
  70 #endif
  71