What’s the function signature need to look like for the first argument of stan::math::hessian?
I have a signature like:
template <typename T_x>
inline const return_type_t<T_x>
f2(const std::vector<T_x> &x)
and the compiler doesn’t like the first argument, gives:
<unresolved overloaded function type>.
How should I define
const F &, the first argument for stan::math::hessian?
This depends whether you are including
math/mix/functor/hessian.hpp, but both of their requirements are documented in the doxygen comment on the function.
For the mix method, you need a function which satisfies:
fvar<var> operator()(const Eigen::Matrix<fvar<var>, Eigen::Dynamic, 1>&)
I think your
f2 would work if changed from using std::vectors to Eigen vectors