Hi rooters.
This is probably a very stupid question. I have fitted a gaussian curve on my histogram and I don’t understand why chi square/ ndf value is so small. I know that such a small value is statistically incorrect.
acq32def.C (3.8 KB)
gaussy.txt (905 Bytes)
gaussfitdef11.pdf (17.0 KB)
I think that maybe is wrong the fit option. I have insered only the “R” option to fit in a specific range. I also tried with another options (like W or L) but I have the same value. What can I do?
When I run your macro I do not get the plot you posted as .pdf file. I get the following:
And the terminal output is:
Processing acq32def.C...
Warning in <HFit::FitObject>: A weighted likelihood fit is requested but histogram is not weighted - do a standard Likelihood fit
FCN=0 FROM HESSE STATUS=FAILED 11 CALLS 131 TOTAL
EDM=0 STRATEGY= 1 ERROR MATRIX UNCERTAINTY 100.0 per cent
EXT PARAMETER APPROXIMATE STEP FIRST
NO. NAME VALUE ERROR SIZE DERIVATIVE
1 Constant -2.00000e+04 1.00000e+00 0.00000e+00 0.00000e+00
2 Mean 0.00000e+00 1.00000e+00 0.00000e+00 0.00000e+00
3 Sigma 0.00000e+00 1.00000e+00 0.00000e+00 0.00000e+00
ERR DEF= 0.5
Hi. I really don’t know why. I just ran the macro to check and i get the pdf. Have you changed the directory of the txt file?
Thank you for answering.
Cheers
Alina
Update: I don’t know why but when i load the txt file here, it changes name from “gaussyy” to “gaussy”.
Hi,
The cause of your small chi2 is the very large error you are having in your histogram. I see in your code you are using TH1::Fill
to set the bin content (calling h->Fill(i, content) ). By doing this you get a bin error equal to the content instead of the sort(content) as you probably should have.
I would suggest you to call h-SetBinContent(i, content)
or if your i does not correspond to histogram bins, then set afterwards the correct histogram errors by calling h->SetBinError
.
Lorenzo
Thank you!!!
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