Skip to main content
Search type Search syntax
Tags [tag]
Exact "words here"
Author user:1234
user:me (yours)
Score score:3 (3+)
score:0 (none)
Answers answers:3 (3+)
answers:0 (none)
isaccepted:yes
hasaccepted:no
inquestion:1234
Views views:250
Code code:"if (foo != bar)"
Sections title:apples
body:"apples oranges"
URL url:"*.example.com"
Saves in:saves
Status closed:yes
duplicate:no
migrated:no
wiki:no
Types is:question
is:answer
Exclude -[tag]
-apples
For more details on advanced search visit our help page
Results tagged with
Search options not deleted user 5010

Complex, contact, Riemannian, pseudo-Riemannian and Finsler geometry, relativity, gauge theory, global analysis.

45 votes

Maps inducing zero on homotopy groups but are not null-homotopic

For a more explicit example than Chris's, consider the map from the (2-dimensional) torus to a sphere that collapses the 1-skeleton of the usual CW complex and takes the 2-cell to the 2-cell of the sp …
Dylan Thurston's user avatar
8 votes
Accepted

Area-preserving map between rectangles and fat polygons

There are lots of ways to do this; without more constraints (or indication of what is desired), it's hard to pick a best one. But here's one. We'll exploit the fact that for any two triangles, there …
Dylan Thurston's user avatar
2 votes

Looking for an introduction to orbifolds

There's another reference I'd like to promote: Orbispaces and their Mapping Spaces via Groupoids: A Categorical Approach, by Coufal, Pronk, Rovi, Scull, and Thatcher, in Women in topology: collaborati …
5 votes

Decomposition of a closed surface

It's the same proof. Take a topological pants decomposition as before, and look for a minimal-length representative on your given Riemannian metric. Then you invoke the theorem that if you have a simp …
Dylan Thurston's user avatar
5 votes
Accepted

Connected components of space of maps between two manifolds

Any continuous map from M to N is homotopic to a smooth map, and if two smooth maps are homotopic, then they are also smoothly homotopic. (More generally, two homotopic functions are homotopic throug …
Dylan Thurston's user avatar
3 votes

Parameterizing rotations of a cube

More useful than embedding it in some higher-dimensional space will be to give it as a manifold with identifications, I think. Topologically, $SO(3)/\!\sim$ is the same space as what you get by taking …
Dylan Thurston's user avatar
1 vote

Automorphism group of formally real Jordan algebras of hermitian matrices

To expand on Michael Orlitzky's answer, unpacking the notation the claim is that, with $h_n(R)$ the $n\times n$ Jordan algebra of Hermitian matrices is $$ \begin{aligned} \mathrm{Aut}(h_n(\mathbb{R})) …