C++ returning a function from within namespace using std::function

I'm trying to return a function using std::function but having typing problems... see code:

#include "LossFunction.hpp"


LossFunction::LossFunction() {
}

LossFunction::LossFunction(int functionType) {
    this->functionType = functionType;
    this->fun = this->getLossFunction();
}
LossFunction::~LossFunction() {

}

std::function<float(Input,Output)> LossFunction::getLossFunction() {
    switch (this->functionType){
        case 0:
            return this->f1;
            break;
        default:
            return this->f1;
            break;
    }
}

I'm getting the following error at compile time:

LossFunction.cpp: In member function ‘std::function<float(Input, Output)>           LossFunction::getLossFunction()’:
LossFunction.cpp:18:17: error: cannot convert ‘LossFunction::f1’ from type     ‘float (LossFunction::)(Input, Output)’ to type ‘std::function<float(Input,  Output)>’
return this->f1;
             ^

LossFunction.cpp:21:17: error: cannot convert ‘LossFunction::f1’ from type ‘float (LossFunction::)(Input, Output)’ to type ‘std::function’ return this->f1;

Any guidance on this issue would be appreciated...

Thanks in advance