https://9lib.org/document/qmjvgjmw-aresimplyrepresentedviathesolutionsofthevelocityhodographequation-thusthevelocityhodographisapowerfultoolforreducingequationsonmanifoldstoequationsinasinglelinearspace-sothatthesolutionsoftheequationson-thatcanbeconstructedfromasecondorderdifferentialequat.html