Donvi

> Would you document this function and add some unit tests? Thanks. This is for unsupported function expm1, which is more accurate than the expression [std::exp](http://en.cppreference.com/w/cpp/numeric/math/exp)(num) - 1.0 if num...

@PHILO-HE , any more comment?

@PHILO-HE thank you for reviewing and fixing, any further comments?

@pedroerp All comments are resolved, so is there any further action needed?