2D histogram subtraction

ROOT
1

Dear Root experts,
Hi !
I have two 2D histograms of identical dimensions (0, 4096) & total bins (4096). I want to subtract ‘hist 2’ from ‘hist 1’ , but only after multiplyig the bin contents of X & Y axis of ‘hist 2’ by factors 0.3 & 0. 2 respectively. Also I want to do this only selectively, i.e. only for those bins of ‘hist 1’, which have non zero entries. I know that In case of a simple subtraction (without any selection) with common multiplying factor (say 0.2) , it can be done in the following way -
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TFile *f1 = new TFile(“f1.root”, “read”);
TH2F h1 = (TH2F)f1->Get(“hist1”);
//
TFile *f2 = new TFile(“f2.root”, “read”);
TH2F h2 = (TH2F)f2->Get(“hist2”);
TH2F h_out = (TH2F)h1->Clone(“difference”);
h_out->Add(h2, -0.2);
h_out->Draw();
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But this selectively subtraction with different factors for X & Y axis is a new problem to me and therefore don’t know how to do it.
So if possible, please suggest me the way to do it with an example.
cylab123

2

You can do something like:

[code]TFile *f1 = new TFile(“f1.root”, “read”);
TH2F h1 = (TH2F)f1->Get(“hist1”);
//
TFile *f2 = new TFile(“f2.root”, “read”);
TH2F h2 = (TH2F)f2->Get(“hist2”);
TH2F h_out = (TH2F)h1->Clone(“difference”);

int nx = h_out->GetXaxis()->GetNbins();
int ny = h_out->GetYaxis()->GetNbins();
for (int i=1;i<=nx;i++) {
for (int j=1;j<=ny;j++) {
double c1 =h_out->GetBinContent(i,j);
if (c1 > 0) {
double c2 =h2->GetBinContent(i,j);
h_out->SetBinContent(i,j,c1-0.2*c2);
}
}
}

h_out->Draw();

[/code]
Rene