MathOverflow is a question and answer site for professional mathematicians. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

Update: I've edited the question, since maybe it was a bit confusing and it's better to start with a more basic question.

I'm looking for properties of Gromov-Hausdorff convergence in the particular case when all metrics $d_n$ and $d$ are defined on a fixed finite or countable set $X$ and they give rise to locally finite spaces.

Fix a point $x\in X$ and denote by $R_x^n$ (resp. $R_x$) the radius of the smallest closed ball, in the metric $d_n$ (resp. $d$), about $x$ which contains at least two points. I suppose that every $(X,d_n)$ is $\delta_n$-connected; i.e. $\delta_n$ is a non-negative real number such that

  1. $|R_x^n-R_y^n|\leq\delta_n$, for all $x,y\in X$

  2. If $\delta'\geq0$ verifies $|R_x^n-R_y^n|\leq\delta'$, for all $x,y\in X$, then $\delta'\geq\delta_n$

  3. For all $x,y\in X$, there is a $\delta_n$-connection; i.e. a finite sequence of points $x_0,x_1,\ldots,x_{n-1},x_n$ such that $x_0=x$, $x_n=y$ and $d(x_i,x_{i-1})\leq\min(R_{x_i}^n+\delta_n,R_{x_{i-1}}^n+\delta_n)$, for all $i=1,\ldots,n$.

Example: connected graph are $0$-connected spaces. If you like, I am just studying deformations of graphs.

Question: Suppose that $(X,d_n)$ is a sequence of $\delta_n$-connected spaces which converges in Gromov-Hausdorff sense to some $(X,d)$. Is it true that $\delta_n\rightarrow\delta$ and $(X,d)$ is $\delta$-connected?

Thank you in advance,


share|cite|improve this question
It would help if you could explain why you need it. So far it seems that you were trying formalize some intuitive idea and made it wrong. – Anton Petrunin Dec 7 '11 at 4:54

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Browse other questions tagged or ask your own question.