ROOFIT yield related question

[sanjay_swain]

Hi,

During UML fit of some distribution i find the fitter gives me yield which is 0.2 +/- 25.0

(the error is 100 times larger)…the EDM is ~ 10^-5 or so… not sure if it is possible for roofit
to give me this large error and fitter still converge? Not sure, if it makes sense ?

-Sanjay

[StephanH]

Hello,

it looks like a failed fit. Have a look at the fit output. Minuit tells you what it thinks of the fit. It looks something like what I pasted below. Already the first four lines are quite instructive …

 MIGRAD MINIMIZATION HAS CONVERGED.
 MIGRAD WILL VERIFY CONVERGENCE AND ERROR MATRIX.
 COVARIANCE MATRIX CALCULATED SUCCESSFULLY
 FCN=4.2579e+06 FROM MIGRAD    STATUS=CONVERGED      37 CALLS          38 TOTAL
                     EDM=4.50916e-07    STRATEGY= 1      ERROR MATRIX ACCURATE 
  EXT PARAMETER                                   STEP         FIRST   
  NO.   NAME      VALUE            ERROR          SIZE      DERIVATIVE 
   1  mean         9.99446e-01   5.77560e-04   8.27114e-05  -8.06984e+00
   2  sigma        1.00036e+00   4.08396e-04   2.04434e-04  -3.35168e+00
                               ERR DEF= 0.5
 EXTERNAL ERROR MATRIX.    NDIM=  25    NPAR=  2    ERR DEF=0.5
  3.336e-07  1.370e-10 
  1.370e-10  1.668e-07 
...