Hi there,
I have trouble with fitting vertical lines with ROOT using Minuit.
I think it comes from the fact that, on a vertical track, the slope of the fit line (defined by y = m*x + b) is infinite.
So, I end up with no fit line drawn and a slope which is crazy big (>10000!).
Maybe, I need to mention that I’m trying to fit TGraphs or TGraphErrors.
I tried to look at the Normal Equation method to maybe solve my problem, but I really don’t understand how it works (and, more importantly, if it’ll work in my situation).
In order to try it out, I slightly modified the file $ROOTSYS/tutorials/matrix/solveLinear.C to build a vertical line (ie all Xs = 1.0 in this case) and I ran it.
As expected, the Minuit method didn’t work and the Normal Equation method seems to give me something, but I don’t know what it is.
When I print the TVectorD (using .Print()) returned by the NormalEqn function, I get :
0 0.858824
1 1
The problem is that I’m not sure what those numbers are.
Could someone help me please ?
Thank you very much.