Questions tagged [compact-manifolds]
For questions regarding the structure and properties of compact manifolds.
246
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A regular, connected, compact surface with curvature on $[0,1]$
today was my final differential geometry exam and there was a problem that I partially solved, but I have some doubts.
The problem asked to prove that there exists a regular, connected, compact ...
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Does every finitely presented group have a finite index subgroup with free abelianisation?
Let $G$ be a finitely presented group. Does there exist a finite index subgroup $H$ such that its abelianisation $H^{\text{ab}} = H/[H, H]$ is free abelian?
Note, if $G^{\text{ab}}$ is not already ...
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$Ric$ flat metric on $S^n$.
Suppose $\mathbb{R}\times S^{n}$ admits a complete riemannian metric $g$ such that $Ric_g = 0$. Prove that this metric $g$ induces a metric $\tilde g$ on $S^{n}$ such that $Rig_{\tilde g} = 0$. So far,...
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Handles have the form $D^λ×D^{m−λ}$
I'm studying Matsumoto's An Introduction to Morse Theory. I want to solve a problem on page 76.
Context: Let $M$ be a closed $m-$manifold and $f:M\rightarrow \mathbb{R}$ a Morse function. Let $c$ be a ...
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U(n) is compact and algebraic, but not abelian—why not a contradiction?
the subgroup of unitary matrices $\text{U}(n) \subset GL(n, \mathbb{C})$ is compact and definitely algebraic, with an algebraic group law; on the other hand, it's not abelian. why is this not a ...
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66
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Lie subgroup of non-abelian compact Lie group is compact?
I need to decide if this statement is true or false:
" Every Lie subgroup of non-abelian compact Lie group is compact."
I think that it is false. I thought in a counterexample in which the ...
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36
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Proof Concerning homeomorphisms of $\mathbb{P}^2$
Is the following proof valid?
CLAIM:
The space obtained by attaching a disc to a Mobius Strip along the boundary is homeomorphic to the projective plane.
PROOF:
We begin by showing that the boundary ...
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Prove that every compact manifold is homeomorphic to a subset of some Euclidean space.
I am trying to prove the following theorem:
Theorem. Every compact manifold is homeomorphic to a subset of some Euclidean space.
The manifolds I'm considering are the most general (without any ...
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2
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1
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84
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Spectral triple on $\mathcal C(M)$ where $M$ is a compact Riemannian manifold, not necessarily spin
I have been reading Alain Connes' Compact metric spaces, Fredholm modules and hyperfiniteness.
In proposition 1, it is mentioned that an unbounded Fredholm module (nowadays: spectral triple) over $C(M)...
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Holomorphic forms are closed on compact manifold $X$ if $\dim(X)=2$.
Let $X$ be a compact complex manifold and $\dim(X)=2$, $\eta$ is a holomorphic form on $X$. Prove that d$\eta=0$.
I know when $X$ is a compact complex Kähler manifold, holomorphic forms are closed.
In ...
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Choice in the non-smooth Whitney Embedding Theorem
Introduction
In Munkres' Topology, he presents a precursor of what seems to be called the non-smooth Whitney Embedding Theorem in Section 50:
Theorem 50.5 (The imbedding theorem). Every compact ...
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Motivation for the definition of a compact Riemann manifold with piecewise smooth boundary
I am asking for either motivation on the requirement regarding $f_i^{-1}(0)$ in the following definition, or better yet a reference to a book dealing with this subject. The following is the definition ...
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Simplicial Homology Groups of Circle Wedge a Torus
Compute the simplicial homology groups of $S^1 \vee (S^1 \times S^1)$ in all dimensions.
I'm trying to practice simplicial homology, and want to make sure I understand at a technical level what's ...
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1
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Fréchet derivative of the total variation norm for measures on a manifold
Let $\Theta$ be a compact $d$-dimensional Riemannian manifold without boundary and $M(\Theta)$ (resp. $M_+(\Theta)$) denote the set of signed (resp. nonnegative) finite Borel measures on $\Theta$.
...
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$S^1\times S^2$ embedded in $\mathbb{R}^4$ [duplicate]
It's easy to embed $S^1\times S^2$ in $\mathbb{R}^5$, since $S^1\subset \mathbb{R}^2$ and $S^2\subset\mathbb{R}^3$, but $S^1\times S^2$ lives also in $\mathbb{R}^4$. How can we write the embedding map ...
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Classify surface given by $abca^{-1}b^{-1}c^{-1}$
I'ven been solving problems from my Topology course, and don't understand something I saw while reading my solved examples. Here's a problem that will let me show my point:
Given $X$ a compact ...
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1
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Proof that a compact surface has a tangent plane orthogonal to position
Given a compact surface $S$, is it true that $S$ has a tangent plane that is orthogonal to the position vector for at least one of its points?
I believe that the statement is true, but I'm having ...
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1
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Subharmonic Functions on Closed Manifolds are Constant?
Apologies in advance if this question is trivial!
Let M be a closed, connected, oriented, n-dimensional, manifold without boundary.
Let $f$ be a smooth function on M where $\Delta f \geq 0$, where $\...
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Regularity of higher order elliptic problem on compact smooth manifolds with boundary
I have trouble in finding a source in the literature for the following result:
Let $\overline{M}$ be a compact smooth manifold of dimension $n \in \mathbb{N}$ with interior $M$ and non-empty boundary $...
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How to deal with boundary orientation in Exercise 16-5 from Lee's Introduction to Smooth Manifolds
16-5. Suppose $M$ and $N$ are oriented, compact, connected, smooth manifolds, and $F,G:M\to N$ are homotopic diffeomorphisms. Show that $F$ and $G$ are either both orientation-preserving or both ...
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Extending an embedding with trivial normal bundle
Let $M^{m}$ and $N^{n}$ be $C^{\infty}$ compact manifold with boundary (eventually $\emptyset$) and let $j:M \to N$ be an embedding such that the normal bundle of the embedding $\nu(j)$ is trivial. ...
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Does there exist a compact submanifold of $\mathbb{R}^3$ whose fundamental group is $\mathbb{Z}^3$?
Does there exist a compact submanifold of $\mathbb{R}^3$ whose fundamental group is $\mathbb{Z}^3$ ?
The question in the title is a generalization of the question that really interests me:
Does ...
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54
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Can a connected closed manifold strictly contain a closed manifold of the same dimension?
A connected closed manifold can contain another one as a proper subset: for instance, the $1$-sphere (circle) is contained in the $2$-sphere. Is it possible with manifolds of the same dimension?
...
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Irreducible triangulations of manifolds
Does there exist a closed Riemann manifold $M$, two distinct irreducible triangulations $S_1$ and $S_2$ of $M$, and a triangulation $T$ of $M$ such that there exists a sequence of edge contractions on ...
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Graph embeddings on nonorientable surfaces
If a finite graph $G$ can be embedded on an orientable surface of genus $n$, does this mean that it can be embedded on a nonorientable surface of genus $n$? Is the converse of this statement true?
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113
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Prove that if $f:M\rightarrow\Bbb R$ is a scalar function over a 1-manifold M without boundary then $\int_M df=0$
Well James Munkres in the text Analysis on Manifolds prove the general Stoke's theorem for $k$-form when $k>1$ and then he proves it for $k=1$ only when the bounary of the Manifold is not empty and ...
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Manifolds with Euler characteristic equal to $\pm 1$
A compact connected smooth surface has Euler characteristic equal to $\pm 1$ if and only it is homeomorphic to the real projective plane or the connected sum of $3$ real projective planes. What are ...
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Can dimension of manifolds be understood similarly to dimension of schemes?
I’m only beginning to learn about schemes, but I know that at least in some cases, the dimension of a scheme (or variety) is 1 less than the length of the longest chain of irreducible closed subsets.
...
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Smooth identification of the complement of a disk
I was wondering, to costruct a map from a compact smooth manifold $M$ of dimesion $n$ to the sphere $\mathbb{S}^{n}$ of degree $1$, apparently, the most common idea is to wrap a disk $D$, neighborhood ...
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76
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Intuitive explanation of degree
I do understand the for $f : \mathbb{S}^{1} \longmapsto \mathbb{S}^{1}$ the degree of a map (thinking $f$ as a closed curve $\gamma$ defined on $[0,1]$) can be seen as "how many times a closed ...
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degree of gauss map for genus $g$ torus in $\mathbb{R}^{3}$
I read that the degree of the gauss map for a $M$ compact orientable $2-$manifold (connected to use the fact that those are only the $g-$torus) in $\mathbb{R}^{3}$ should be $(1-g)$, which is $\frac{1}...
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Could exists a vector field on $\mathbb{S}^{2}$ with exactly $n$ zeroes?
I just started to learn index theory of tangent vector fields. I'm aware of two examples on the sphere $\mathbb{S}^{2}$ with exactly one zero, which, which are $F(x,y) = (1-x^2-y^2)\partial x$ thought ...
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Compact hyperbolic three-manifold - a question
In a recent paper the authors considered a spacetime described by
$$AdS_4 \times \Sigma_3 \times \mathcal{I}_r \times S^2$$
where $\mathcal{I}_r$ is an interval of the $r$-coordinate and the two-...
user494842
3
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2
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Homotopy invariance for compactly supported cohomology
I can't find any reference regarding homotopy invariance for compactly supported cohomology and I wonder under which conditions the homotopy invariance still holds for compactly supported cohomology.
...
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1
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144
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Uniformization theorem for $C^k$ surfaces?
Does the uniformization theorem apply for surfaces that are $C^k$ ($k<\infty$)? I'm familiar with a couple of proofs of Uniformization (using Riemann-Roch, Ricci flow). But most of these proofs ...
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Is there an example of reducible compact 3-manifold with boundary that has no embedded incompressible two-sided surface?
There is a theorem stating that for irreducible compact manifolds with non-empty boundary there always exists such an embedded surface and I'm trying to understand why the irreducibility condition ...
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1
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59
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Making intuition rigorous that integral of some positive function on set should be monotone in the Haar measure of the set
Let $\mathcal{M}$ be a compact Riemannian manifold with geodesic distance function $d$ and $\Omega$ its volume measure.
Pick some $A,B\subseteq\mathcal{M}$ such that $\Omega(A)\ll\Omega(B)$, but: (1) $...
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Covering $\Bbb RP^\text{odd}\longrightarrow X$, what can be said about $X$?
I am looking for any argument related to the following fact, which may or may not be true.
Let $f:\Bbb RP^n\longrightarrow X$ be a covering space, where $n\geq 2$. Then, $X=\Bbb RP^n$.
Now, for $n=\...
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Compactification of log z Riemann Surface
I've been reading the 'Road to Reality' book of Roger Penrose and in the chapter on Riemann Surfaces, there is a note that we can compactify the log z Riemann Surface into a sphere. But I don't see ...
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What is the "natural homomorphism" in the definition of an *essential manifold*?
The following definition of "essential manifold" is in this wiki page:
A closed $n$-manifold $M$ is called essential if its fundamental class $[M]$ defines a nonzero element in the homology ...
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Simplicial complexes embedded on a compact manifold
Every finite graph can be embedded on some compact surface of sufficient genus such that no two edges cross. If $S$ is a finite simplicial complex of dimension $n$, can $S$ be embedded in some ...
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Can all connected graphs be embedded on a closed, compact 2-Manifold?
I know that there are spherical (planar) graphs such as $K_4$,and toroidal graphs such as $k_7$, but I was wondering if given any connected graph $G$, there exists a closed, compact 2-Manifold $M$ ...
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An orientable surface that cannot be embedded into $\Bbb R^3$?
By Whitney's embedding theorem, every 2-dimensional manifold (aka. a surface) can be embedded into $\Bbb R^4$.
Now, the Wikipedia page on that theorem states in this paragraph that we can even embedd ...
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intersection number on the boundary of a manifold
Let $F: W \to N$ be a smooth map, where $W$ is a compact manifold with boundary, $Z \subset N$ is closed and all manifolds are oriented. Also $\partial F \pitchfork Z$ and
$F^{-1}(Z)$ is a compact, ...
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668
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The Sobolev embedding inequality on manifolds
Let $(M,g)$ be a (smooth) compact Riemanian manifold of dimension $n$. I expect that the following inequality is true for any smooth function $f$:
$$(\int_{M} |f|^{\beta})^{1/\beta} \leq C \;(\int_{M}...
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157
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square root of a Riemannian metric
Let $(M,g)$ be a compact Riemannian manifold. Taking a smooth vector field $X$, there is an associated smooth function $$g(X,X):M\longrightarrow \mathbb{R}^+, \quad p\longmapsto g_p(X_p,X_p)\geq 0.$$ ...
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158
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Proof of classification theorem for compact surfaces
I am reading Massey's 'A basic coruse in Algebraic Topology'. In first chapter, he proved classification theorem for compact surfaces (compact connected 2-manifold). This theorem classifies compact ...
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Can one characterize compact smooth manifolds dynamically as such?
If $M$ is a smooth (connected) compact manifold, then it is known that any (smooth) vector field is complete, which means that the flow exists for all $t \in \mathbb{R}$.
What about the converse? If $...
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The relationship between the tubular neighbourhoods of two diffeomorphic manifolds
I'm a beginner of this complex area and want to use the differential geometry as a tool to solve some control problems. So my statement might be a little bit inaccurate...I will try my best.
There ...
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Is a pentagon a surface?
My question arise since a pentagon is homeomorphic to a closed disc. This last one is a surface with boundary.
However, a pentagon has vertices, so it seems isn't a 2-manifold.
If you consider a ...
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