All Questions
8 questions
12
votes
1
answer
327
views
What are the extremal CAT(0) metrics?
(Split off from Does every CAT(0) space embed in a measurable integral of $\mathbb{R}$-trees? )
Fix an integer $k \ge 2$, and let
$MC0_k \subset \mathbb{R}^{\binom{k}{2}}$ be the set of possible ...
- 10.1k
11
votes
1
answer
498
views
Is the center of gravity in a CAT(0) space contained in the convex hull?
In reading Greg Kuperberg's partial answer to this question Convex hull in CAT(0) ,
I started wondering if the center of gravity is always contained in the closed convex hull.
More precisely, given $...
- 10.1k
7
votes
1
answer
246
views
Rigidity for convex surfaces in elliptic/hyperbolic space
From Alexandrov's work we know that any metric on the sphere with lower curvature bound $\kappa$ (in the sense of Alexandrov) can be realized as a closed convex surface (i.e. boundary of a compact ...
- 115
6
votes
2
answers
210
views
Geodesics on convex hypersufaces
Let $M^n$ be the boundary of a convex compact set in $\mathbb{R}^{n+1}$ with non-empty interior.
Question 1. Is $M$ geodesically complete, i.e. is it true that every geodesic (= locally shortest path)...
- 21.8k
6
votes
1
answer
148
views
Isometric imbedding of a 2-disk into Euclidean 3-space
Let us call a cap the intersection of the boundary of 3-dimensional convex compact set $K$ in $\mathbb{R}^3$ with a half-space bounded by a plane $H$ such that the orthogonal projection to $H$ of this ...
- 21.8k
5
votes
1
answer
348
views
Hausdorff vs Gromov-Hausdorff convergence of convex hypersurfaces
Let $\{K_i\}$ be a sequence of convex compact $n$-dimensional subsets in a Euclidean space $\mathbb{R}^n$. Assume $\{K_i\}$ converges in the Hausdorff metric to a convex compact set $K$ which is also $...
- 21.8k
3
votes
1
answer
118
views
Is a cap an Alexandrov space?
Let us call a cap the intersection of the boundary of 3-dimensional convex compact set $K$ in $\mathbb{R}^3$ with a half-space bounded by a plane $H$ such that the orthogonal projection to $H$ of this ...
- 21.8k
3
votes
1
answer
163
views
A.D. Alexandrov imbedding theorem for metrics with symmetry
A well known theorem due to A.D. Alexandrov says that any metric on the 2-sphere $S^2$ with curvature at least -1 (in the sense of Alexandrov) can be isometrically realized either as convex surface in ...
- 21.8k