{
  //http://www.slac.stanford.edu/BFROOT/www/doc/workbook/root1/root1.html


 int indA=3;
//put on x axis the mass of the particle for example
 float xA[indA]={250,500,750};
//on the y axis put the number you want to plot for each particle mass
 float yA[indA]={0.25,0.3,0.6};
// then here - fill in the errors for the x and the y points
 float xeA[indA]={0,0,0};
 float yeA[indA]={0,0,0};

 graphA = new TGraphErrors(indA, xA, yA, xeA, yeA);
 graphA->SetMarkerStyle(4);
 graphA->SetMarkerSize(0.7);
 graphA->Draw("APL");



// leg = new TLegend(0.6,0.7,0.89,0.89);  //coordinates are fractions
//                                          //of pad dimensions
//   leg->AddEntry(graphA,"First histo","l");  // "l" means line
//                                             // use "f" for a box
//   leg->Draw();
//   // oops we forgot the header (or "title") for the legend
//   leg->SetHeader("The Legend Title");
//   leg->Draw();
}