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Zapiski Nauchnykh Seminarov POMI, 2013, Volume 415, Pages 24–28
(Mi znsl5682)
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On the space of convex figures
V. V. Makeev, N. Yu. Netsvetaev St. Petersburg State University, St. Petersburg, Russia
Abstract:
Let $T$ be the set of convex bodies in $\mathbb R^k$, and let $\mathcal T$ be the set of classes of similar bodies in $T$. We write $F$ for $T$ in the case $k=2$. Define a metric $d$ on $\mathcal T$ by setting for classes $\{K_1\},\{K_2\}$ (from $\mathcal T$, of convex bodies $K_1,K_2$) $d(\{K_1\},\{K_2\}) =\inf\{\ln(b/a)\}$, where $a$ and $b$ are positive reals such that there is a similarity transformation $A$ with $aA(K_1)\subset K_2\subset bA(K_1)$. Let $D_2$ be a planar unit disk. If $x>0$, we denote by $F_x$ the set of the planar convex figures $K$ in $F$ with $d(\{D_2\},\{K\})\ge x$. We also equip the sets $T$ and $F$ with the usual Hausdorff metric.
We prove that if $y>\ln(\operatorname{sec}(\pi/n))\ge x$ for some integer $n>2$, then no mapping $F_x\to F_y$ is $\operatorname{SO}(2)$-equivariant.
Let $M_k (n)$ be the space of $k$-dimensional convex polyhedra with at most $n$ hyperfaces (vertices), and let $M_k$ denote the space of $k$-dimensional convex polyhedra. We prove that there are no $\operatorname{SO}(2)$-equivariant continuous mappings $M_k(n+k)\to M_k(n)$.
Let $T^s$ be the closed subspace of $T$ formed by centrally symmetric bodies. Let $T_x$ denote the closed subspace of $T$ formed by the bodies $K$ with $d(T^s,\{K\})\ge x>0$. We prove that for every $y>0$ there exists an $x>0$ such that no mapping $T_x\to T_y$ is $\operatorname{SO}(2)$-equivariant.
Key words and phrases:
convex figure, convex body, orthogonal group, vector bundle, Grassmannian.
Received: 31.12.2012
Citation:
V. V. Makeev, N. Yu. Netsvetaev, “On the space of convex figures”, Geometry and topology. Part 12, Zap. Nauchn. Sem. POMI, 415, POMI, St. Petersburg, 2013, 24–28; J. Math. Sci. (N. Y.), 212:5 (2016), 533–535
Linking options:
https://www.mathnet.ru/eng/znsl5682 https://www.mathnet.ru/eng/znsl/v415/p24
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Abstract page: | 219 | Full-text PDF : | 51 | References: | 33 |
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