void fcn(int &npar, double *gin, double &f, double *par, int iflag)
{
    double x = par[0], y = par[1];
    f = pow(x-2.,2)+pow(y-3.,2);
}

void example_01()
{
    TMinuit *gMinuit = new TMinuit(2);
    gMinuit->SetFCN(fcn);
    gMinuit->DefineParameter(0, "x", 8. , 1., 0., 0.);
    gMinuit->DefineParameter(1, "y", 6. , 1., 0., 0.);
    
    gMinuit->Command("MIGRAD");
    gMinuit->Command("MIGRAD");
    
    double x,y,xerr,yerr;
    gMinuit->GetParameter(0,x,xerr);
    gMinuit->GetParameter(1,y,yerr);
    
    printf("x: %+.7f +- %.7f\n",x,xerr);
    printf("y: %+.7f +- %.7f\n",y,yerr);
}