# Division of two histograms

Dear Experts

I would like to divide two histograms h2 by h1. Following two histograms which I am dividing are as follows in the order of h1 and h2. My ROOT macro (where I am trying to divide them) is also attached along with the two Root files. Please check if the method I am following is correct as the output histogram should be close to 1 with mean value around 0.999

Please fill also the fields below. Note that root -b -q will tell you this info, and starting from 6.28/06 upwards, you can call .forum bug from the ROOT prompt to pre-populate a topic.

ROOT Version: Not Provided
Platform: Not Provided
Compiler: Not Provided

draw_Performance.C (2.5 KB)
bremge2v.root (516.8 KB)
totdeposit.root (3.8 KB)

The code seems ok. Maybe Divide does not do what you think/want; see the source code for Divide.

I also checked the resulting histogram everything is correct.
Since h1 and h2 are more or less the same you obtain a flat distribution with height close to 1.
And for a flat distribution like yours you have for mean and std dev.

\mu=\frac{b-a}{2}\sim \frac{10-0}{2}\sim5\\ \sigma=\sqrt{\frac{b^2-a^2}{12}}\sim\sqrt{\frac{10^2-0^2}{12}}\sim2.89

And the statistics of the histogram you obtain match with these numbers.

Maybe you are referring to the distribution of the histogram bins content that should have a mean close to 1.

Actually the output histogram should be like the following after taking the ratio between total energy and photon energy I think you are confused about how Divide works. What it does is that it takes the content of bin #1 of one histogram, divides it by the bin content of bin #1 of another histogram and puts this ratio in bin #1 of a new histogram. Rinse and repeat for all bins.

However, what you want is probably dividing the x-values of two histograms. But this is not what Divide does.

Thanks kindly suggest how I can divide x-values of two histograms

How would you do that by hand, if you didn’t have software? I don’t know what that means exactly, and maybe you don’t either. Perhaps yus can give you the code to what s/he meant by that, but you will not have learnt much (then again, maybe that’s fine with you, but I think it’s better to learn something ). My suggestion: first of all, think about it, come up with a well-defined problem and a well-defined solution, how you would do it by hand (test it if you must), and then see if there’s already a way to do that in ROOT, or write the code yourself. As it is now, I don’t think you have expressed clearly what you are trying to do and how. You first said “I would like to divide two histograms h2 by h1”; and it would seem that Divide does something like that, but depends on what you really mean, so…

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