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 7311

Euclidean, hyperbolic, discrete, convex, coarse geometry, metric spaces, comparisons in Riemannian geometry, symmetric spaces.

32 votes
5 answers
6k views

What is a good method to find random points on the n-sphere when n is large?

As part of a more complex algorithm, I need a fast method to find random points of the n-sphere, $S^n$, starting with a RNG (random number generator). A simple way to do this (in low dimensions at lea …
Dick Palais's user avatar
  • 15.3k
27 votes

$C^1$ isometric embedding of flat torus into $\mathbb{R}^3$

On the other hand, if you are willing to settle for conformally flat, there is a beautiful theory of these. (The idea is to consider flat embeddings in the three-sphere, and then "project them into $R …
Dick Palais's user avatar
  • 15.3k
18 votes
1 answer
859 views

What sort of models did Bolyai and Lobachevsky use to demonstrate the consistency of their m...

As is well-known, in the 1820s both Bolyai and Lobachevsky showed, at long last, the independence of the Parallel Postulate from the rest of the axioms of Euclidean geometry by developing what we now …
Dick Palais's user avatar
  • 15.3k
16 votes

Shortest-path Distances Determining the Metric?

There is an old paper of mine called "On the Differentiability of Isometries" in which I show that if you know a Riemannian manifold $M$ only as a metric space, i.e., you just know its point set and t …
Dick Palais's user avatar
  • 15.3k
6 votes

Intuitive proof that the first $(n-2)$ coordinates on a sphere are uniform in a ball

I find myself very confused by all this, and I suspect I must be missing something very important, and I am hoping someone (Greg?) can set me straight. Let's just consider the classic case $n=3$, so …
Dick Palais's user avatar
  • 15.3k
5 votes

Easy proof of the fact that isotropic spaces are Euclidean

There is a classic paper by Jordan and von Neumann where they prove results that allows this question is settled in an elementary way. On Inner Products in Linear, Metric Spaces Author(s): P. Jordan …
Dick Palais's user avatar
  • 15.3k
2 votes

History of the triangle inequality

Here is a suggestion, to get the idea across in an informal way---it is what I always tell the students when I introduce the triangle inequality: I tell them that its essential content, and the way it …
Dick Palais's user avatar
  • 15.3k