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Jun 21, 2016 at 6:31 comment added user35593 It is also discussed here: mathoverflow.net/questions/96532/…
Jun 20, 2016 at 19:54 comment added Michael Renardy Yes, with $H^{1/2}$ the inequality holds.
Jun 20, 2016 at 19:51 comment added user35593 Ok, now I understand your argument. Can we say that the inequality holds with $L^\infty$ replaced by $H^{1/2}$?
Jun 20, 2016 at 19:44 vote accept user35593
Jun 20, 2016 at 19:05 comment added Christian Remling Why was this downvoted? It may be a bit terse, but Michael is making a very valid point. You can also consider concrete examples such $u(z)=\textrm{Re}\exp ((z+1)/(z-1))$ on the unit disk (and approximate $\phi$ in $L^1$ by continuous functions) to see that what you were hoping for is false.
Jun 20, 2016 at 17:39 comment added Michael Renardy Just to be clear: What I am saying it that if $\phi$ is in $L^\infty$ and not in $H^{1/2}$, then the solution to Laplace's equation (or to any other equation) is not in $H^1$.
Jun 20, 2016 at 17:28 comment added Michael Renardy Regardless of what equation is satisfied, the regularity of the boundary data does not improve over what is given!
Jun 20, 2016 at 17:15 comment added user35593 Here we have not just a H1 function but the harmonic map for which we can expect higher regularity. I do not see why it should not be possible.
Jun 20, 2016 at 15:33 history answered Michael Renardy CC BY-SA 3.0