Save a histogram

ROOT
1

ROOT Version: 5.34/36
Platform: lxplus
Compiler: Not Provided

I want to do histogram division in PyRoot but couldn’t do it. Then I tried to save them as Root files, and everything works basically well, except that I still couldn’t do the division in Root, regardless of treating them as histograms or pointers.

2

Histograms’division can be performed thanks to the Divide method. Is it the technique you were trying to use ?

3

Yes, and it shows

Error: Symbol Dec is not defined in current scope  (tmpfile):1:
Error: Symbol Dec is not defined in current scope  (tmpfile):1:
(const int)0
*** Interpreter error recovered ***

And I’ve also tried using “/” directly and it doesn’t work as well

4

It seems you are trying to access some undefined object (Dec).
Can you provide a small script reproducing your problem ?

5 
root [0] TFile f("Histograms.ROOT")
root [1] Dec->Draw()
Info in <TCanvas::MakeDefCanvas>:  created default TCanvas with name c1
root [2] ->Divide(Dec,Dec)
Error: Symbol Dec is not defined in current scope  (tmpfile):1:
Error: Symbol Dec is not defined in current scope  (tmpfile):1:
(const int)0
*** Interpreter error recovered ***

I just draw Dec to make sure it really exists and is a histogram. “Histograms.ROOT” is a file I created in PyRoot to store my histograms.

6

Your Divide line is wrong. You need to do:

result_histogram->Divide(Dec,Dec);

See the help…:

Replace contents of this histogram by the division of h1 by h2.

this = c1h1/(c2h2)

By the way Dec divided by Dec should give a predictable result equal to 1.

7 
root [3] result_histogram->Divide(Dec,Dec)
Error: Symbol result_histogram is not defined in current scope  (tmpfile):1:
Error: Failed to evaluate result_histogram->Divide(Dec,Dec)
*** Interpreter error recovered ***

That’s what I’ve got…Do I need to define result_histogram first?

8

Yes you need to create an histogram in order to call the Divide method on it.

9

Great, seems it works. Thank you!

10

Yes it must work :slight_smile:

11

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