Fit a function by minuit

Hi Root Experts

I would like to use Minuit to fit a function(not a histogram or a graph…)
say the function f = f( x, y)
and vary the parameter x, y to get f as close as a value f0

Is there any similar example to do this?

I tried to use the example(root/test/minexam.cxx) in user guide
The first problem I have is how to “SetFCN” ?
Is there any certain format for the FCN?

Thank you very much,

Have a look at

and in particular