For the functional IL(v,λ)≡Iv(v)+∫ΩcλG(v)dxdy, what is the necessary condition for IL to have a stationary value?
(a) δvxIL+δvyIL+δλIL=0
(b) δvxIL-δvyIL-δλIL=0
(c) δvxIL-δvyIL+δλIL=0
(d) δvxIL+δvyIL-δλIL=0
I have been asked this question in final exam.
This intriguing question comes from Penalty in section Flows of Viscous Incompressible Fluids of Finite Element Method