Root Minuit Fitting Discrepancy: Mac versus Linux installation

Hello,

Let me preface and say that I am quite green at root; I have had very little experience up until about 3 weeks ago, so I apologize

I have code that I am running to extract two fit parameters from a .root data file. The code works perfectly fine on any Mac OSX root installation. Iâ€™ve tried versions: 6.19/01, 6.16/00, 6.14/06, 6.14/00 on three different MacBooks running Mojave, and everything runs fine and spits out numbers that we agree with.

Because we are preparing to ramp up some simulations and analysis, weâ€™ve set up an Ubuntu 18.06LTS server and have built and installed root there. Here is where the crux of the problem lies: We run the macro on this root installation - same exact code, same exact data - and now the fitting portion spits out this error.

``````FUNCTION VALUE DOES NOT SEEM TO DEPEND ON ANY OF THE 2 VARIABLE PARAMETERS.
VERIFY THAT STEP SIZES ARE BIG ENOUGH AND CHECK FCN LOGIC.
*******************************************************************************
*******************************************************************************
FUNCTION VALUE DOES NOT SEEM TO DEPEND ON ANY OF THE 2 VARIABLE PARAMETERS.
VERIFY THAT STEP SIZES ARE BIG ENOUGH AND CHECK FCN LOGIC.
*******************************************************************************
*******************************************************************************
****************************************
Chi2                      =       73.565
NDf                       =           46
Edm                       =  1.07836e-11
NCalls                    =          196
#sigma_{mp}               =      671.619   +/-   1.37259      	 (limited)
T                         =      293.068   +/-   3.94207      	 (limited)

Covariance Matrix:

#sigma_{mp}           T
#sigma_{mp} 	       1.884     0.57166
T           	     0.57166      1.1072

Correlation Matrix:

#sigma_{mp}           T
#sigma_{mp} 	           1     0.39581
T           	     0.39581           1

``````

and the values we get are in the general realm of what we want , but not what we expect. Iâ€™ve installed the same versions of root (all separately sourced in local directories and terminal instances, mind) and I get the same error and weird fit parameters. Looking into this error, it has been suggested that for some reason Minuit is finding some region where the gradient is 0 and thus that is confusing Minuit into thinking there is a minimum there, and that I should try limiting the parameter range fed to Minuit to exclude that problem region. I do, and the error goes away, but the values are even more off. I also donâ€™t necessarily find that reasoning convincing, considering this works completely fine on one instance of root (mac) and not the other(ubuntu), so something is not-defined correctly or a library is being used somewhere where another one would be better.

IGNORE THIS ~~~Looking in some of the root documentation, I came across THIS where it suggests that there are two versions of the Tformula class and they are not necessarily compatible. Iâ€™m wondering if on the Mac root it is using the cling-based one and on ubuntu it is using the cint-based, but I am such a novice at root that I really cannot say much more and am kinda at a loss at where to proceed. ~~~~~

Looks as if CINT has been deprecated for quite awhile, so this explanation makes no sense. Which means I am even more at a loss.

Any help or pointers would be greatly appreciated!