Let \(G\) be an open subset of \(\mathbb {R}^N\) and let \(f\in L^2(G)\). Show that \(f\) defines a continuous linear
functional on \(H^1(G)\).
State the Lax-Milgram theorem for subspaces \(V\subset H^1(G)\).
Show that the Lax-Milgram theorem may be applied to the form \[ a(u,v)=\sum _{i=1}^{N}\int _G \partial _i u\,\partial _i\overline {v} +\int _G u\overline {v} \] and \(f\) as
above.
Assume that \(G\) is a bounded open set with “very smooth” boundary and let
\(u\) be the Lax-Milgram solution just determined. What partial differential
equation (in the sense of distributions) will be solved by \(u\) and what
boundary conditions does \(u\) satisfy (please give an argument to prove the
latter)?