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A branch of geometry dealing with convex sets and functions. Polytopes, convex bodies, discrete geometry, linear programming, antimatroids, ...

6 votes
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Are the polyhedral cones the only examples of cones that remains closed when they are added ...

The radial cone of $C$ is defined via $$ \mathcal R_C(x) := \bigcup_{\lambda > 0} \lambda ( C - x)$$ for all $x \in C$ and we can show $$ \mathcal R_C(x) = C + \operatorname{span}(x), $$ since $C$ is …
gerw's user avatar
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2 votes
Accepted

A converse question about the polyhedrality under linear mapping

I think we can argue as in https://mathoverflow.net/a/423284/32507 to answer the question in the affirmative. Let $\mathcal R_K(x)$ be the radial cone of $K$ at $x$ (as defined in the other answer). F …
gerw's user avatar
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2 votes
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When are infimal convolutions contractions?

Here are just some thoughts. I think it is a matter of curvature, so let us assume that $\varphi$ and $\psi$ are smooth. Then, $y(x)$ solves the optimality condition $$ \psi'(y(x)) = \varphi'(x - y(x) …
gerw's user avatar
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0 votes

On faces of polytopes

The set $K_A$ is essentially a polar of $A$. Indeed, we have $$ A = \{ x \in \mathbb R^n \mid l(x) \ge t \; \forall (l,t) \in K_A\} =: B.$$ The inclusion "$\subset$" is clear and in order to check "$\ …
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