avoid recomputation. f_a/g_a has already been computed and we can use it directly. Change-Id: I39b07205c7d2486e88076089fa960f116919f27f
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.