Kato inequality

Asked Oct 20 '12 at 23:47

Active Jan 09 '13 at 17:57

Viewed 916 times

For any real-valued smooth function $u$, we have the Kato inequality

$|\nabla|\nabla u||^2\leq(\operatorname{trace}(\operatorname{Hess}(u)))^2$,

which holds when $|\nabla u|\neq0$.

If moreover $u$ is harmonic (in an open set in $\mathbb{R}^n$), how would the Kato inequality be improved to

$|\nabla|\nabla u||^2\leq\frac{n−1}{n}(\operatorname{trace}(\operatorname{Hess}(u)))^2$ ?

edited Jan 09 '13 at 17:57

asked Oct 20 '12 at 23:47

Miranda

It should be worth mentioning that this was also asked at MO link – Ben Jan 14 '13 at 22:21
3

This question has been asked on MO and has answers there. – Michael Albanese Dec 14 '14 at 02:12

0 Answers0