Trouble getting x axis values using Tspectrum

[Nisha]

Hello,

This might be a simple question but I am not very familiar with root yet so I am having trouble figuring this out.
I have a plot with multiple peaks in it. I am using Tspectrum to find the peaks and I need the x axis values for which I am using GetPositionX() command. However, this command is giving me incorrect values to x. Maybe it is giving the channel no but I need the user-defined values i.e. I need to read the values from the plot. I am attaching a pdf of the data.
Background subtracted data.pdf (110.5 KB)

So for example, the x value of first peak should give me something like 29 but I am getting 197 which is clearly incorrect. Can anyone help with this? Here is the part of the code -

TSpectrum *mySpec = new TSpectrum();

Int_t npeaksFound = mySpec->Search(hTVsC_backsub, 20," ",0.1);

Double_t *xpeaks = mySpec->GetPositionX();

Double_t x[npeaksFound];

for(Int_t iter = 0; iter<npeaksFound; iter++ ) {

cout << xpeaks[iter] << endl;

}

cout << "No. of Peaks found is = " << npeaksFound << endl;

I really appreciate your help. Thank you for your time

_ ROOT Version:* 6.18/04
Platform:* C++
Compiler:* Visual Studio Code

[Wile_E_Coyote]

Try:
std::cout << hTVsC_backsub->GetXaxis()->GetBinCenter(1 + Int_t(xpeaks[iter] + 0.5)) << std::endl;

[Nisha]

Thank you for getting back so quick. I tried using the command you sent, it still is giving incorrect values. This is what it produces-

-183.667
-172.836
-177.759
-226.501
-161.266
-155.85
-166.682
-145.019
-135.172
-149.45
-194.499
-189.329
-125.325
-121.879
No. of Peaks found is = 14

I don’t know how to proceed. Thank you for your time! Appreciate it!

[Wile_E_Coyote]

Try:
std::cout << hTVsC_backsub->GetBinCenter(1) + xpeaks[iter] * hTVsC_backsub->GetBinWidth(1) << std::endl;

[Nisha]

Still gives similar values, changed by some decimal numbers.

[Wile_E_Coyote]

What values do you get from the original (post the full list):

@Nisha

cout << xpeaks[iter] << endl;

[Nisha]

I get these numbers -
197.158
241.222
221.036
22.6231
287.502
310.396
265.593
353.722
394.093
336.243
152.847
173.525
434.219
447.512
No. of Peaks found is = 14

These are not correct. The actual number should be something
25
152 and so on (Just by reading the graph visually after zooming in)

[Wile_E_Coyote]

It looks like you have the correct values.
Note that the peaks are “ordered” according to their “heights”.

[Nisha]

Wait,
I think it is giving me the correct values but they are not in order of the peaks in the plot. The values check out with reading the x axis by zooming in the plot. It’s just that the first value is not for the first peak. I have no idea how to fix that though. Let me know if you have any suggestions on that!
Ha! Thank you so much @Wile_E_Coyote. I really appreciate your time and help. Thank you again!

[Nisha]

Haha! Yeah, I was typing the same thing! Thank you so much! You have been very helpful! Appreciate it!
Have a great day!