When using printlevel=3 the result of each iteration is printed. You have :
FVAL : function value for that iteration
EDM: expected distance from the minimum. This is the quantity used for the convergence of the iteration. When is smaller than tolerance the minimisation is stopped
Nfcn :: number of function calls
Error matrix change: how much the error matrix changes in the iteration
Parameters: value of the fit parameters (variables of the function to be minimised). The user value is printed (Minuit applies internally a transformation)
The signature is
bool Scan(unsigned int i , unsigned int & nstep , double * x , double * y , double xmin , double xmax);
i is the parameter index
nstep: is the number of points to scan
x is the returned array with the scanned x points
y is the array with the returned y values
xmin is an optional parameter with the minimum parameter value to scan
xmax is the maximum parameter value.
In case xmim and xmax are not given the scan will be done in +/- 2 error on the parameter
Sorry if the documentation is not clear on this. I will fix it.
You can call Scan after having done the minimisation. For example you can do this to scan the parameter ipar
int npoints = 20;
minimizer->Scan( ipar, npoints, &x, &y );
TGraph * g = new TGraph(points, &x, &y );
If you still have problems using Scan, I can send you an example
Thank you very much for your response. If I understand Scan correctly, it will scan parameter number ipar near its minimum a total of npoints away and return those corresponding parameter values and LogLikelihood values (x, and y arrays respectively). Is this right?
I seem to be getting an error when I implement the function call of Scan. I have done almost exactly as you have suggested:
int npoints = 20;
@moneta This is very helpful. However, I have a simple question as the documentation is brief to the point of being a bit confusing. What does “Covariance was made pos defined” mean? Specifically, what does the phrase “was made pos defined” mean? I would assume this means that it was forced to be positive definite, so is “defined” a typo? Or am I misunderstanding what is trying to be conveyed.