Aligning two histograms by shifting bins

Newbie
1

Hello users,

I have two histograms that are shifted by some factor

image
image1609×894 11.1 KB

Is it possible to shift the bins of one wrt to the other to align them?

So far, I am having the centroids of the peaks for both the histograms obtained by fitting. The ultimate goal is to align these centroids such that the peaks overlap.

I am a new user with minimal experience in these operations, so any suggestion will be precious.

Thanks in advance

2

It is possible in principle, see Can we shift histogram for several channels? - #2 by Pepe_Le_Pew

1 Like
3

Hi @yus ,

Thanks a lot for pointing to the valuable thread.

I think I should scale the contents, however from the documentation it seems function TH1::Scale only changes the contents by a multiplicative factor this = this*c1

Is it possible to change the contents by this = this*c1 + c2
c2 is a constant offset

4

I think you have to change the X-axis values, not the Y-axis ones. TH1::Scale changes the Y-axis values.

1 Like
5

Yes, you are correct.
I think I should use the

ScaleXaxis(hist1, ScaleX);

However, doing so gives an error.

ScaleXaxis(his1, Scale)


ROOT_prompt_396:1:18: error: cannot initialize an array element of type 'void *' with an rvalue of type 'Double_t (*)(Double_t)' (aka 'double (*)(double)')

The function scale

#include "TAxis.h"
#include "TH1.h"
#include "TArrayD.h"

Double_t Scale(Double_t x)
{
  Double_t v;
  v = 10 * x + 100; // "linear scaling" function example
  return v;
}

Can you please suggest what I am messing up here ?

6

Can you show your full the code? You should have three functions defined (ScaleX, ScaleAxis, ScaleXaxis), and call the latter in your own code.

7

Ya, my bad I did not copy the whole code. Now it seems to work.

Thanks a lot for your help and time.