#include "TGraph.h"
void TestGraphSort()
{

// This program sorts the following 9 numbers, in groups of 3.    


//Int_t m;

Float_t x[9]={3.0, 2.0, 1.0, 6.0, 5.0, 4.0, 9.0, 8.0, 7.0};
Float_t y[9]={30.0,20.0,10.0,60.0,50.0,40.0,90.0,80.0,70.0};
Double_t *px, *py;
// Tgraph::Sort() works ok in the following indivisual calls.

TGraph *graph=new TGraph(9,x,y);
graph->Sort(&TGraph::CompareX,kTRUE,0,2);
graph->Sort(&TGraph::CompareX,kTRUE,3,5);
graph->Sort(&TGraph::CompareX,kTRUE,6,8);

px=graph->GetX();
py=graph->GetY();

for (Int_t i=0; i<9;i++) printf("x=%2.1f  y=%2.1f \n ",*(px+i),*(py+i));

print("\n");

//However, if TGraph::Sort() is called in a while-loop or in an if-loop (as shown below), segmentation occurs if run in interpreted mode:
//	 >>.x TestGraphSOrt.c
// It seems to run OK in compiled mode:
//  >>.x TestGraphSort.c+

TGraph *graph1=new TGraph(9,x,y);

for(Int_t m=0;m<3;m++){

graph1->Sort(&TGraph::CompareX,kTRUE,3*m,3*(m+1)-1);
}

px=graph1->GetX();
py=graph1->GetY();

for (Int_t i=0; i<9;i++) printf("x=%2.1f  y=%2.1f \n ",*(px+i),*(py+i));

}