Is this action a Hamilton's principal function? Posted by Milou, at physics.stackexchange.com, 08 Oct 2016 In Ref. 1, in section 3, they wrote: \begin{equation} L'(q,\dot{q},\ddot{q},t)~=~L(q,\dot{q},\ddot{q},t)-\frac{dS(q,\dot{q},t)}{dā¦