const int Npoints = 3;  // Number of points in the graph
const double x[Npoints] = {1.0, 2.0, 5.0};
const double y[Npoints] = {0.5, 1.0, 2.0};
const char  *c[Npoints] = {"a","b","c"};

void graphtext3() {
   TGraph *gr = new TGraph(Npoints, x, y);
   gr->SetMarkerStyle(kCircle);
   TExec *ex = new TExec("ex","DrawText();");
   gr->GetListOfFunctions()->Add(ex);

   gr->Draw("ALP");
   gr->GetXaxis()->SetLabelSize(0);
   gr->GetXaxis()->SetTickLength(0);
}


void DrawText()
{
   Int_t i,n;
   Double_t x,y;
   TLatex *t;
   TLine *l;

   TGraph *g = (TGraph*)gPad->GetListOfPrimitives()->FindObject("Graph");
   double ymin = g->GetHistogram()->GetMinimum();
   double ymax= g->GetHistogram()->GetMaximum();
   double dy = (ymax-ymin);
   n = g->GetN();
   for (i=0; i<n; i++) {
      g->GetPoint(i,x,y);
      t = new TLatex(x, ymin-0.03*dy, Form("%s (%4.2f,%4.2f)",c[i],x,y));
      t->SetTextSize(0.025);
      t->SetTextFont(42);
      t->SetTextAlign(21);
      t->Paint();
      l = new TLine(x,ymin,x,ymin+0.03*dy);
      l->Paint();
   }
}