Update the minimum required version of Eigen to 3.3. Change-Id: I6e6bd745311b7d4f1d5b749ec70d314f9e765438
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.