Questions tagged [rigidity]
The rigidity tag has no usage guidance.
17 questions with no upvoted or accepted answers
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Is the dodecahedron flexible (as a polytope with fixed edge-lengths)?
Consider the (regular) dodecahedron $D\subset\Bbb R^3$. I want to continuously deform it so that throughout the deformation
it stays a convex polytope,
it stays a combinatorial dodecahedron (i.e. its ...
- 13.6k
13
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Is a convex polyhedron determined by its edge lengths and angular defects?
Let's consider 3-dimensional convex polyhedra $P\subset\Bbb R^3$.
The angular defect at a vertex $v$ is $2\pi$ minus the sum of the interior angles of the incident faces at $v$.
Question:
Is a ...
- 13.6k
11
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Definition of a uniformly bounded dual of a group
The unitary dual of a group $G$ is the set of equivalence classes of irreducible unitary representations of $G$ with the Fell topology. (This topology is defined using convergence of positive definite ...
user2412
4
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Conformal $L^p$ rigidity of Riemannian manifolds
$\newcommand{\M}{\mathcal{M}}$
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$\newcommand{\CO}[1]{\text{CO}(#1)}$
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Examples of rigid open surfaces
In the celebrated book of Hilbert and Cohn-Vossen, the following sentence appears (p. 230):
Bending is impossible in the case of all closed convex surfaces, such as, for example, the ellipsoids. It is ...
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3
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Tannaka duality for Hopf algebroids
Setting. Let $k$ be a field, $A$ a finite-dimensional $k$-algebra, and $H$ a Hopf algebroid over $A$ with invertible antipode. Denote by $\operatorname{mod}(H)$ the category of finite-dimensional ...
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Rigidity vs Super-rigidity of representations (of Kähler/surface groups)
In the literature there are several definitions of "rigidity" (or "super-rigidity") of representations, adapted to the circumastances. I wonder what are the relations between them; I excuse in advance ...
- 301
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Regarding rigid graphs in the plane
Quoting from the book (page 272) Graphs and Geometry by Lovasz, we have the following theorems regarding the characterization of rigid graphs in the pane.
Theorem 1: A graph $G$ is rigid in the plane ...
- 1,305
2
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Right unitor in star-autonomous categories
1.Context
Let $(C, \otimes, I, a, l,r)$ be a monoidal category. Here $r$ denotes the right unitor.
Suppose $S: C^{op} \xrightarrow{\sim} C$ is an equivalence of categories with inverse $S’$. Assume ...
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$l$-adic rigidity for Milnor $K$-theory
Given a local henselian ring $A$ with the maximal ideal $m$, does the quotient map $A\mapsto A/m$ induce isomorphisms on $l$-adic Milnor $K$-theories? ($K_n^M(R)\otimes \mathbb{Z}_l$, where $l$ is an ...
- 5,901
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Infinitesimal rigidity vs local rigidity of isometrically immersed riemannian manifolds
I was reading the nice survey on rigidity, focusing on tensegrities by Connelly, and I'd like to know the status and feedback about a question he asks:
A theorem by Gluck and this work of Connelly, ...
- 2,041
2
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Are a map with constant singular values and its inverse always conjugate through isometries?
Let $U \subseteq \mathbb R^2$ be open, connected and bounded, and let $0<\sigma_1<\sigma_2$ satisfy $\sigma_1 \sigma_2=1$.
Suppose that $f:U \to U$ is a diffeomorphism whose singular values (of $...
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Rigidity of Diophantine torus translations
Let $T_a:x\mapsto x+a$ be a Diophantine translation on the torus $\mathbb T^d$, $d>1$.
Let $h$ be some $C^1$ diffeomorphism of $\mathbb T^d$ such that
$$
g=h\circ T_a\circ h^{-1}
$$
is $C^\infty$. ...
- 4,188
1
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Ways of proving that a framework is locally rigid
Given a (bar-and-joint) framework/linkage, I would like to know what are possible ways of showing that the framework is locally rigid. Also, what is known about the computational complexity of ...
- 1,305
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The rigidity of $2$-dim sphere with constant sectional curvature in $\mathbb{R}^n$ for $n> 3$
If there is a smooth isometric embedding $f: (S^2, g)\rightarrow \mathbb{R}^n$, where $(S^2, g)$ is a sphere with Riemannian metric such that the corresponding sectional curvature is equal to $1$, and ...
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Frameworks in general position that are locally rigid but not infinitesimally rigid
The classical theorem of Asimow and Roth says that for a generic framework (i.e., coordinates of the nodes are algebraically independent), local rigidity and infinitesimal rigidity are equivalent. I ...
- 1,305
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Which polytopes can be folded to an edge?
While playing with bar-and-joint linkages, I noticed that the skeleton of a regular 3-dimensional cube can be folded to a single edge (this can be achieved by first flexing the cube to bring it to a ...
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