TH1 Scaling with errors

ROOT
1

I want to work out a subtraction of two histograms of the form:
h1+=-c1*h2
I can perform this with TH1::Add and that I should use TH1::Sumw2 to calculate histogram bin errors before scaling or addition.
However my factor c1 has an error itself I wish to include.
Do either of TH1::Scale or TH1::Add include this functionality? (As far as I can tell they do not)
Is there already a way of doing this or is the best option to set the bin errors manually?
Thanks
James S

2

Hi James,

Here is a suggestion. You could create a new histogram with bin contents set to the value of your constant and its bin errors set to the constant’s error. I think you can then use the TH1::Multiply(TH1*) method to properly propagate the errors.

Otherwise, you can just brute force write the error propagation routine that computes the result for each bin.

Hope that helps.

3

Thanks for the suggestion.
Worked nicely than doing it entirely manually.
James S