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Aug 4, 2013 at 3:37 comment added Deane Yang BS, thanks but I wasn't claiming that any determined elliptic PDE of higher order satisfies UCP. Just that you can find sufficient conditions for UCP for an overdetermined system using known sufficient conditions (whatever they might be) for a determined system.
Aug 3, 2013 at 20:52 comment added BS. @Deane : but there are counterexamples (by Plis and then by Hormander, if I remember right), of fourth order linear elliptic operators with smooth coeffs and without the UCP. But presumably not of the form $P^*P$, so the question remains open (and badly phrased).
Aug 3, 2013 at 4:17 comment added Deane Yang Have you tried googling "elliptic pde system unique continuation"? This seems to yield some papers that seem relevant. Also, if $P$ is an overdetermined elliptic PDO, then $P^*P$ is a determined elliptic PDO and it seems likely to me that $P$ satisfies the UCP if and only if $P^*P$ does. So it might suffice to consider only determined elliptic operators.
Aug 3, 2013 at 4:03 comment added user38064 I cannot use Holmgren's theorem, because it requires real-analytic coefficients. It is a system of PDE for one real-valued function, but each one of those equations is alone not elliptic.
Aug 3, 2013 at 4:00 history edited user38064 CC BY-SA 3.0
I added the definition of overdetermined ellipticity.
Aug 2, 2013 at 17:37 answer added Bazin timeline score: 3
Aug 2, 2013 at 13:11 comment added Ben McKay So you have two elliptic PDEs, or one elliptic and one something else, or more than two? I think that if you already have one elliptic PDE, you should be able to apply: Aronszajn, N. A unique continuation theorem for solutions of elliptic partial differential equations or inequalities of second order.
Aug 2, 2013 at 12:51 comment added Liviu Nicolaescu You need to specify what you mean by overdetermined. Many but not all classes of eliptic systems satisfy the unique continuation property.
Aug 2, 2013 at 12:23 comment added BS. What do you mean exactly by overdetermined ? Is $P$ vector (or complex) valued ?
Aug 2, 2013 at 10:49 comment added Michael Renardy Is there any reason you cannot use Holmgren's theorem?
S Aug 2, 2013 at 10:42 history suggested Branimir Ćaćić CC BY-SA 3.0
LaTeX and grammar cleanup
Aug 2, 2013 at 10:01 review Suggested edits
S Aug 2, 2013 at 10:42
Aug 2, 2013 at 8:27 review First posts
Aug 2, 2013 at 11:03
Aug 2, 2013 at 8:09 history asked user38064 CC BY-SA 3.0