// macro to test graphs

#include "TCanvas.h"
#include "TGraph.h"
#include "TH1.h"
#include "TMath.h"

void Graph()
{
   TCanvas *canvas = 0;
   canvas = new TCanvas("c1","A Simple Graph Example",200,10,700,500);

   const Int_t n = 2000000;
   Double_t x[n], y[n];
   for (Int_t i=0;i<n;i++) {
     x[i] = i*10.0/n;
     y[i] = 10*sin(x[i]+0.2);
   }

   Double_t fMinX = TMath::MinElement(n, x); fMinX -= fMinX/10.0;
   Double_t fMaxX = TMath::MaxElement(n, x); fMaxX += fMaxX/10.0;
   Double_t fMinY = TMath::MinElement(n, y); fMinY += fMinY/10.0;
   Double_t fMaxY = TMath::MaxElement(n, y); fMaxY += fMaxY/10.0;

   TH1F *frame = 0;
   frame = canvas->DrawFrame(fMinX, fMinY, fMaxX, fMaxY);
   frame->SetTitle("a simple graph");
   frame->SetXTitle("X title");
   frame->SetYTitle("Y title");
   frame->GetXaxis()->CenterTitle(kTRUE);
   frame->GetYaxis()->CenterTitle(kTRUE);

   TGraph *graph = 0;
   graph = new TGraph(n, x, y);

   graph->SetBit(kCanDelete);    //delete from TPad
   graph->SetMarkerStyle(1);
   graph->SetMarkerColor(1);
   graph->SetLineStyle(1);
   graph->SetLineColor(2);
   graph->Draw("P");  //option "A" (axis) not allowed if axes set with DrawFrame

   // TCanvas::Update() draws the frame, after which one can change it
   canvas->Update();
   canvas->Modified();
}