Add missing includes pair_hash.h uses std::size_t and std::hash but does not include the corresponding headers <cstddef> and <functional>. Change-Id: I194a5c76e8f50b1574e1359f616351581033c576
Ceres Solver is an open source C++ library for modeling and solving large, complicated optimization problems. It is a feature rich, mature and performant library which has been used in production at Google since 2010. Ceres Solver can solve two kinds of problems.
Please see ceres-solver.org for more information.