Add the Quaternion manifold and tests. Change-Id: I0a396a5834168c1526d6f2b8c99a1ad3348ad657
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.
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