Im currently trying to do a fit of my 2 dimensional model to a binned data set. The model currently has 5 fit parameters and im doing the fit with Minuit2. Unfortunately two of those fit parameters make the fit process problematic and Minuit quits with this message:
Info in : VariableMetricBuilder: no improvement in line search
VariableMetric: Iteration # 14 - FCN = -13532121.09988 Edm = 0.203166 NCalls = 224
Info in : VariableMetricBuilder: iterations finish without convergence.
Info in : VariableMetricBuilder : edm = 8.29717
Info in : requested : edmval = 2e-05
Info in : VariableMetricBuilder: FunctionMinimum is invalid after second try
As far as I understand it would mean that my minimization space (5 dim) is rather flat because of these two troublesome parameters and Minuit cannot determine the edm precisely. Hence it will also not fit a correct minimum. How is the edm actually calculated? Currently Im trying to plot my minimization space (loglikelihood space) in those two troublesome dimensions in the area of my minimum. Hopefully that can give some hints on whats going wrong. My model computation is rather complicated, so the I might have some numerical instability issue here. Any ideas?