Strange failed fitting

Roofit and RooStats
1

Dear experts,

I have a quite simple model, and I fit it to data. I see some parameters get to be nan through the fitting procedure:

Parameter values: ATLAS_norm_Wl=-nan, ATLAS_norm_Zl=-nan, alpha_ATLAS_LUMI_2012=-nan, alpha_SysstopWtNorm=-nan, alpha_SysttbarNorm=-nan, gamma_stat_Region_Y2012_isMVA0_B4_J2_T0_L0_distAnyVar_TType_bin_0=-nan, gamma_stat_Region_Y2012_isMVA0_B4_J2_T0_L0_distAnyVar_TType_bin_1=-nan, gamma_stat_Region_Y2012_isMVA0_B4_J2_T0_L0_distAnyVar_TType_bin_2=-nan, gamma_stat_Region_Y2012_isMVA0_B4_J2_T0_L0_distAnyVar_TType_bin_3=-nan
RooRealIntegral::alpha_SysstopWtNormConstraint_Int[nom_alpha_SysstopWtNorm][ Int alpha_SysstopWtNormConstraintdAna ]

Before, I also see :

[#0] WARNING:Minization – RooMinimizerFcn: Minimized function has error status.
Returning maximum FCN so far (14.8992) to force MIGRAD to back out of this region. Error log follows
Parameter values: ATLAS_norm_Wl=1.00517, ATLAS_norm_Zl=1, alpha_ATLAS_LUMI_2012=0, alpha_SysstopWtNorm=0, alpha_SysttbarNorm=0, gamma_stat_Region_Y2012_isMVA0_B4_J2_T0_L0_distAnyVar_TType_bin_0=1, gamma_stat_Region_Y2012_isMVA0_B4_J2_T0_L0_distAnyVar_TType_bin_1=1, gamma_stat_Region_Y2012_isMVA0_B4_J2_T0_L0_distAnyVar_TType_bin_2=1, gamma_stat_Region_Y2012_isMVA0_B4_J2_T0_L0_distAnyVar_TType_bin_3=1

I debugged for quite some time, but still no idea … could anyone help ? Please look the attached log file and workspace.

Thanks a lot!
Javier
Test.root (55.2 KB)
log.txt (490 KB)

2

Hi Javier,

these errors usually occur in presence of a model which are not sanely defined for all values of the parameters, e.g. with parameters at the denominator, under square root and so on.
Did you check this?

Danilo

3

Dear Danilo

Thanks a lot for the idea! Unfortunately the model is built using HistFactory and not by-hand from me. I have checked the numbers in the xml file carefully, all the up/down variations look reasonable to me …

Would you know some un-sane cases that can come from HistFactory ?

Thanks.

Javier

4

Hi Javier,

unfortunately not. Not that I am aware of.
Is the model once written on paper as a formula sane?

Danilo