void readGr() {

TGraph *gr = new TGraph("graph.dat");// read txt file

TCanvas *c1 = new TCanvas();

gr->SetLineColor(2);

gr->SetLineWidth(4);

gr->SetMarkerColor(4);

gr->SetMarkerStyle(21);

gr->SetTitle("Draw graph from ASCII file");

gr->GetXaxis()->SetTitle("X title");

gr->GetYaxis()->SetTitle("Y title");

gr->Draw("LAP"); //A -> Axis P->Point L->Line(Default)

}