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3 votes

Uniqueness of solution to heat equation when initial condition is a generalized function

(Not sure if I understand the question correctly.) If $p_{t,x}(y) = p(t, x, y)$ is the fundamental solution (a.k.a. the heat kernel), then $p_{t,x}$ converges as $t \to 0^+$ to the Dirac measure $\del …
Mateusz Kwaśnicki's user avatar
3 votes
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Unique continuation of the Hilbert transform

No. Let $$u(z) = \exp(-(-iz)^{1/2}-(-iz)^{-1/2})$$ for $z$ in the closed upper complex half-plane, with the principal branch of the complex power. Then $u$ is a bounded holomorphic function in the ope …
Mateusz Kwaśnicki's user avatar
5 votes
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Uniqueness of minimizers in the Calculus of Variations

There's no uniqueness in general. If $\Omega$ is a unit square, and $$\varphi(x, y) = (1-x-y)^+,$$ then obviously any $u$ which is decreasing with respect to both $x$ and $y$, and which matches the bo …
Mateusz Kwaśnicki's user avatar