Fix the build breakage caused by the last commit. Change-Id: I0145c7008e8272f4b7f3ce9134dd3e7128d9059a
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.