TMinuit interactive mode

Dear all,

in the old FORTRAN version, Minuit had an interactive mode to which one could switch during program execution and which allowed the user to interactively control a fit (fixing and releasing parameters, minimizing, etc.)

I tried to obtain this behaviour inside ROOT, using TMinuit. I called something like

Indeed, Minuit reports


when I run the program, but continues non-interactively. Is there any way to get into the interactive mode using the ROOT framework?




The interactive functionality of the old Fortran version is not supported and it is not needed now in C++.
In ROOT you can run in interactive mode from the ROOT prompt using CINT where you can then issue all the command you want to Minuit.

Best Regards


Hi Lorenzo,

thank you very much for the clarification. I still do not see how I can (without a lot of effort) get similar possibilities with ROOT and CINT as with the old Fortran interactive mode. This is probably more of a general question on CINT than on Minuit.

Is there an example somewhere which shows how I can interactively pass commands via the prompt during execution of my program (without terminating it before, and, of course without having to implement this myself)? How can I return to my running program after having interactively passed commands to Minuit, so that my program can continue running, using the results obtained interactively?

Thanks in advance,


Hi Jens,

from the ROOT prompt you can execute any method or function of your program. In the case of Minuit, you can issue all the Minuit commands, using for example gMInuit->Command( " …") or gMinuit->mnexcm. This is exactly the same functionality available in the interactive Fortran version.


Hi Lorenzo,

hmm, I am probably lacking a bit of general understanding here. My situation is the following:

I have a large program which does many things. At some point, it has to perform a fit which occasionally requires some manual intervention. After the fit, the program continues, using the result of the fit and many other results obtained before. So when I arrive at the fit, I need to quit my program to return to the CINT prompt and issue interactive Minuit commands, right? But once I have quit the program, I cannot return to it later on without having lost all earlier results. Of course I can somehow store them before quitting, but this requires a lot of additional code.

How would you deal with a case like that?

Thanks and sorry for this beginner question,