How to set 'error in SetBinError'

[SAYAN_CHATTERJEE]

Hello everyone.
I am trying to use SetBinError, but little bit confused about the error analysis formula. I have three histograms h1, h2, h3. They have same binning.

TH1D* hr
double nbins = h1->GetNbinsX();
for( int i = 0; i< nbins; i++)
{
   double get_h1 = h1->GetBinContent(i+1);
   double get_h2 = h2->GetBinContent(i+1);
   double get_h3 = h3->GetBinContent(i+1);
   double get_setcontent = (h1 - (h2*h3));
   hr -> SetBinContent(i+1, get_setcontent);

   double geterror_h1 = h1->GetBinError(i+1);
   double geterror_h1 = h1->GetBinError(i+1);
   double geterror_h1 = h1->GetBinError(i+1);
   double error1 = (geterror_h1 - (geterror_h2*geterror_h3));
   double error2 = ( geterror_h1 - (geterror_h2*get_h3) - (get_h2*geterror_h3) );
   hr -> SetBinError(i+1, error1 or error2 ); ????????????????????????????????????
} 

What should be the correct SetbinError? error1 or error2 or something else?

Thank you
Sayan

[oshadura]

@couet can you please take a look?

Thank you in advance,
Oksana

[couet]

I guess it is up to you to decide what the errors should be.

[yus]

Hi Sayan,

what does the following do exactly?

@SAYAN_CHATTERJEE

double get_setcontent = (h1 - (h2*h3));

Are you trying to manipulate histograms in a loop over bins? Or are these bin contents of three different histograms?

Also, why nbins is a double and not an int here:

@SAYAN_CHATTERJEE

double nbins = h1->GetNbinsX();

?

[SAYAN_CHATTERJEE]

@SAYAN_CHATTERJEE

   double get_setcontent = (h1 - (h2*h3));

Hi yus,

Thanks. These are the typing mistake! These are the bin contents of these three histograms!
It should be " double get_setcontent = (get_h1 - (get_h2*get_h3));"
And you are right, nbins is integer variable.

Can you please suggest the proper error formula for the above equation?

@SAYAN_CHATTERJEE

   hr -> SetBinError(i+1, error1 or error2 ); ????????????????????????????????????

For this line.

Thanks
Sayan

[yus]

I’m not sure this is correct, but I’d do something like this:

const double overallRelativeUncertainty = TMath::Sqrt(TMath::Sq(geterror_h1/get_h1) + TMath::Sq(geterror_h2/get_h2) + TMath::Sq(geterror_h3/get_h3));
hr->SetBinError(i+1, overallRelativeUncertainty * get_setcontent);

[SAYAN_CHATTERJEE]

Thanks yus,

I’d definitely check with this

Sayan.