摘要：The variational formulation of boundary value problems is valuable
in providing remarkably easy computational algorithms as well as an
alternative framework with which to prove existence results.
Boundary conditions impose constraints which can be annoying from a
computational point of view. The question is then posed: what is the
most general boundary value problem which can be posed in
variational form with the boundary conditions appearing naturally?
Special cases of two-point problems in one-dimension and some higher
dimensional problems are addressed. There is a deep connection with
self-adjointness for the linear case. Further cases under which a
Lagrangian may or may not exist are explained.
