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_ROOT Version:6.22

*Platform:* Not Provided

*Compiler:* Not Provided

Hi,

i need to use class and operator() rather than function as bellow:

original code:

```
double RosenBrock(const double *xx )
{
const double x = xx[0];
const double y = xx[1];
const double tmp1 = y-x*x;
const double tmp2 = 1-x;
return 100*tmp1*tmp1+tmp2*tmp2;
}
```

Which is input in the `ROOT::Math::Functor f(&RosenBrock, 2);`

, means that it has 2 parameters. When I changed the function to class, I got an error.

```
class RosenBrock {
public:
double xx;
double operator() (double *xx ) {
// function implementation using class data members
const double x = xx[0];
const double y = xx[1];
const double tmp1 = y-x*x;
const double tmp2 = 1-x;
return 100*tmp1*tmp1+tmp2*tmp2;
};
}
RosenBrock r;
ROOT::Math::Functor f(r, 2);
```

```
In module 'MathCore':
/home/sima/Products/root/include/Math/Functor.h:120:14: error: no matching function for call to object of type '__cling_N524::RosenBrock'
return fFunc(x);
^~~~~
/home/sima/Products/root/include/Math/Functor.h:90:4: note: in instantiation of member function
'ROOT::Math::FunctorHandler<ROOT::Math::Functor,
__cling_N524::RosenBrock>::DoEval' requested here
FunctorHandler(unsigned int dim, const Func & fun ) :
^
/home/sima/Products/root/include/Math/Functor.h:428:17: note: in instantiation of member function
'ROOT::Math::FunctorHandler<ROOT::Math::Functor,
__cling_N524::RosenBrock>::FunctorHandler' requested here
fImpl(new FunctorHandler<Functor,Func>(dim,f) )
^
input_line_55:8:21: note: in instantiation of function template specialization
'ROOT::Math::Functor::Functor<__cling_N524::RosenBrock>' requested here
ROOT::Math::Functor f(r, 2);
^
input_line_52:16:11: note: candidate function not viable: 1st argument ('const double *') would lose const
qualifier
double operator() (double *xx ) {
^
```

Do you have any idea to fix it?

thanks in advance