In his book on optimal control, George Leitmann uses a meaning of "Jacobian determinant" I don't understand (and I do understand the standard definition). Can anyone explain it? In particular, which function's Jacobian is being taken? (Also, why? I understand this why bit might be hard without more context.) The relevant excerpts from the book are, in order:
(Unfortunately, I don't have access to "Ref 6.1").
EDIT: I'm not requiring a firm answer like "This is definitely what it means." Even conjecture is fine.