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.
Update: I don’t know why but when i load the txt file here, it changes name from “gaussyy” to “gaussy”.
Yes the filename was not correct I get it now:
@moneta will know.
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
This topic was automatically closed 14 days after the last reply. New replies are no longer allowed.