# Martin

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# 242 Actions

 Jan25 asked If A $\subset S^n$ has spherical diameter < $\pi$, then $S^n - A$ contains a closed semisphere. Dec19 comment Distinction between 'adjoint' and 'formal adjoint' These lines on Wikipedia only describe the construction for a differential operator. I have been concerned about general operators and their formal adjoints. Nov16 awarded Yearling Nov8 asked Correct term for trivial extension of linear operator on Hilbert spaces Nov2 comment Solid angle between vectors in n-dimensional space Your second formula is quite awkward, because you apply arctan against a vector. Oct27 accepted Is the Empty set an orientable manifold? Oct27 asked Is the Empty set an orientable manifold? Jul28 awarded Popular Question Jul19 revised Bound the pseudo-inverse matrix of a product Typo Jul18 comment Proof by Induction $n^2+n$ is even You know you don't need induction, do you? Jul18 asked Bound the pseudo-inverse matrix of a product Jul11 comment Minimizer of $p$-average of distances to points $x_1,\dots,x_n$ @ChristianBlatter: A name, like some exotic mean, would be helpful, of course. Jul11 comment Minimizer of $p$-average of distances to points $x_1,\dots,x_n$ @Paul: Yes, by definition. The vector $D$ is just a formal device. Jul11 asked Minimizer of $p$-average of distances to points $x_1,\dots,x_n$ Jul7 answered How to use Galerkin approximation to find the existence of weak solution. Jul6 accepted The Betti numbers of a triangulated ball relative to a disk in its boundary Jul6 revised The Betti numbers of a triangulated ball relative to a disk in its boundary clarification Jul6 asked The Betti numbers of a triangulated ball relative to a disk in its boundary Jun20 asked Slobodeckij and Bessel definitions of fractional Sobolev spaces on Lipschitz domains May24 asked Example for $\Omega$ so that $\partial\Omega \neq \partial\bar{\Omega}$