Strange failed fitting

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!
Test.root (55.2 KB)
log.txt (490 KB)

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?


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 ?



Hi Javier,

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