Questions tagged [smooth-manifolds]

For questions about smooth manifolds, a topological manifold with a maximal smooth atlas.

A topological manifold of dimension $n$ is a Hausdorff, second countable topological space $X$ such that each $x \in X$ has a neighbourhood homeomorphic to an open subset of $\mathbb{R}^n$.

A smooth atlas on a topological manifold $X$ is a collection of pairs $\left\lbrace(U_{\alpha}, \varphi_{\alpha})\right\rbrace_{\alpha\in A}$ where $U_{\alpha}$ is an open subset of $X$ and $\varphi_{\alpha} : U_{\alpha} \to \varphi_{\alpha}(U_{\alpha}) \subseteq \mathbb{R}^n$ is a homeomorphism such that $\bigcup\limits_{\alpha\in A}U_{\alpha} = X$.

A topological manifold with a maximal smooth atlas is called a smooth manifold.

6282 questions
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Definition of smooth submanifold

This question may be repetitive and I have read some questions on the definition of submanifolds, but I was not satisfied with the answers. There are some types of submanifolds---immersed, embedded, and regular, as far as I know, and the first…
Behrooz
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Smooth Manifolds, differentiability a counterexample

I have just proved that: Given $M, M', N, N' $ smooth manifolds and $f : M \longrightarrow M'$ and $g : N\longrightarrow N'$ are differentiable k class maps then: $f \times g : M \times N \longrightarrow M' \times N'$ is a differentiable k class map…
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Construct a smooth partitions of unity subordinate to the open cover $U$

Let $U= \{ (-n,n): n=1,2,3 . . . \}$ be an open cover for $\mathbb{R}$. I need to construct a smooth partitions of unity subordinate to the open cover $U$ . Now, I know from the definition that I need to find a collection of functions…
Dark_Knight
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Gluing two smooth 1-manifolds

I am reading the book on 2D topological quantum field theories by Joachim Kock and I am confused with the example on gluing two smooth 1-manifolds. It is on page 38-39 of the book. Take two smooth 1-manifolds, $M_0$ and $M_1$. They have common…
Jerry
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Boundary of a sublevel

Let $f: B_1(0)\subset\mathbb{R}^2 \to \mathbb{R}$ be a smooth function, and say $c\in \mathbb{R}$ is not a critical value of $f$. Is it true that each connected component $\Gamma$ of $\left\{f\le c\right\}$ has $\partial \Gamma = \emptyset$? Or…
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Defining submanifolds without charts

In his elegant 2012 introduction to smooth manifolds, Nigel Hitchen minimizes his reliance on charts. In stating what it means for a manifold $M$ to be a smooth submanifold of $N$, for example, he gives the condintion that $D\iota_x$ is injective…
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Quotient by a distribution/foliation?

Suppose we have a (smooth) manifold $M$, and an integrable smooth distribution $\Delta$ on $M$. Somewhere, I read that we can define a natural map $\pi:M \rightarrow \frac{M}{\Delta}$. First of all, what should I understand by $\frac{M}{\Delta}$? I…
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Is a vector field a closed map?

A smooth vector field $V$ on a smooth manifold $M$ is a smooth section of the projection $\pi : TM \rightarrow M$. (This means that $V \colon M \rightarrow TM$ satisfies $\pi \circ V = \text{id}_M.$) Does $V$ map closed sets to closed sets? My…
Open Season
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Why derivations obey chain rule.

Let $X, Y, Z$ be smooth manifolds and suppose we have smooth maps $$ F:X\to Y, $$ $$ G:Y\to Z. $$ By derivation at $x\in X$ I mean a linear map $$ \mathfrak{d}:C^\infty(X) \to \mathbb{R}, $$ such that for any $f_1,f_2\in C^\infty(X)$ we have…
Jimmy R
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Identity between a differential map and its differential.

In the Do Carmo book's Riemmanian Geometry say: Observe that if $\phi:M\rightarrow M$ is a differential map, $v\in T_p M$ and $f$ is a real differentiable function in a neighborhood of $\phi(p)$, we have $$(d\phi(v)f)\phi(p)=v(f\circ \phi)(p)…
EQJ
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Confusions on Pullback

I am reading Lee's book Introduction to Smooth Manifold. I am confused about the conception of pullback in this book. Assume $F:M\to N$ is a smooth map. We can define a pullback $F^*$ at $p\in M$ associated with $F$ such as $$F^*:T^*_{F(p)}N\to…
gaoxinge
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Smooth maps into an immersed submanifold

Quote An introduction to manifolds: In the pictures $f(t) = (\cos t,\sin 2t)$ and $g(t) = (\cos t,−\sin 2t)$ I'm completely confused here, he is proving that $\overline{f}$ is not continuous if $S$ has the induced topology from $g$. But this…
mez
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Smoothness of Product Functions

Suppose $f:\mathbb{R}^{n}\times\mathbb{R}^k\to\mathbb{R}$. Define $$f(x,y)\equiv f_x(y)\equiv f_y(x)$$ If $f_x$ and $f_y$ are both smooth, is $f$ smooth?
Dave
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is a differentiable function is necessarily a smooth one

i know that each smooth function is differentiable which follows from the fact that if partial derivatives exist at each point in a domian then f is differentiable everywhere on that domain. but does the converse true i.e. is a differentiable…