Dividing one axis of a TH3D by a TH1D

Newbie
1

Hi root experts, newbie question:

I have a TH3D and I want to divide only one axis by a TH1D, while leaving the other axes unaffected. How do I do this?

So far I’ve tried:

  void normalisation() {

    TFile *file = new TFile("~/Desktop/somepath/data.root","read");
    TH3D* histo3D_Original = (TH3D*)file->FindObjectAny("histo_3D");
    TH1D* histo1D= (TH1D*)file->FindObjectAny("histo_1D");
    
    TCanvas *canvas1 = new TCanvas();
    canvas1->Divide(2,2);
    
    canvas1->cd(1);
    histo3D_Original->Draw("colz");

    canvas1->cd(2);
    histo1D->Draw("colz");
    
    TH3D* histo3D_Clone = (TH3D*)histo3D_Original->Clone("histo3D_Clone");
    histo3D_Clone->GetYaxis()->Divide(histo1D->GetXaxis,1);
    
    canvas1->cd(3);
    histo3D_Clone->Draw("colz");
    
    file->Close();
    
    }

Which gives me the error message:

error: no member named 'Divide' in 'TAxis'
    histo3D_Clone->GetYaxis()->Divide(histoFlux->GetXaxis,1);

Any ideas? Thanks!

2

Yes, TAxis has no members Divide().

3

Which means there is no way to accomplish what I’m trying to achive?

4

I am not sure what that mean exactly. “Dividing an axis by an histogram” looks a bit weird seems to me. May be @moneta will have some idea about it.

5

Please indicate exactly which mathematical operation you would like to do.
The division is done at the bin level, i.e. you divide the bin content(x,y,z) of the 3D histogram

Lorenzo

6

This might already help me. By saying ‘dividing an axis by a histogram’ I mean that I want to take all the y bins of the 3D histogram and divide them by all the x bins of the 1D histogram, using the ->Divide function.

Maybe a little bit more detail: The y axis of the TH3D describes the energy of a particle, which needs to be normalized by the flux, which is described by the x axis of the TH1D.

7

Still I am confused. There are no y bins in a 3D histograms. A bin is having an x, y and z component. You might want to project (i.e. summing) for a given x all the corresponding bins or perform an average (Profile).

Also you seem to want to normalize coordinates ( y values). Instead in an histogram you normalize only bin contents (the 4th component in a 3d histogram).

I would suggest you describe with mathematical formulae what would you like to do

Lorenzo