...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
template <int R,int C> static inline scalar_type & write_element( Matrix & m );
This function template is expected to be static member of user-defined specializations of the mat_traits template. It returns mutable reference to the element at row R and column C of m.