About intersections of TGraph(s)

ROOT
1

I have this part of the code:

 Int_t nop=100;
 Double_t xpt, ypt, del = 0.9975/nop;

 TGraph *av1 = new TGraph();

 for (Int_t j=0; j < nop; j++)
 {
  xpt = del*j + 0.0025*del;
  av1->SetPoint(j, xpt, 0.0);
 }

 for (Int_t i=0; i<nof; i++)
 {
  for (Int_t j=0; j < nop; j++)
  {
   av1->GetPoint(j, xpt, ypt);
   av1->SetPoint(j, xpt, ypt + fpf[i]->Eval(xpt)/(Double_t)nof);
  }
 }

 TGraph *av2 = new TGraph();

 for (Int_t j=0; j < nop; j++)
 {
  xpt = del*j + 0.0025*del;
  av2->SetPoint(j, xpt, 0.0);
 }

 for (Int_t i=0; i<nof; i++)
 {
  for (Int_t j=0; j < nop; j++)
  {
   av2->GetPoint(j, xpt, ypt);
   av2->SetPoint(j, xpt, ypt + ebu[i]->Eval(xpt)/(Double_t)nof);
  }
 }

 TGraph *av3 = new TGraph();

 for (Int_t j=0; j < nop; j++)
 {
  xpt = del*j + 0.0025*del;
  av3->SetPoint(j, xpt, 0.0);
 }

 for (Int_t i=0; i<nof; i++)
 {
  for (Int_t j=0; j < nop; j++)
  {
   av3->GetPoint(j, xpt, ypt);
   av3->SetPoint(j, xpt, ypt + ebd[i]->Eval(xpt)/(Double_t)nof);
  }
 }

i wanted to get the value in the x-axis of the point of intersection between graphs av1 & av2 and av1 & av3. how will i do that? thanks for your help…

2

@moneta can you give a hand with this one?

1 Like
3

Hi,

As far as I know we don’t have a function in ROOT to find the intersection between two Graphs. You have probably to write yourself an algorithm that find the intersection point using from example Graph::Eval.

In case of linear TGraph, you might assume that locally, there is some example code available here

Lorenzo

4

gracias… @moneta :slight_smile:

5

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