19,555 reputation
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bio website math.rice.edu/~andyp
location Houston, TX
age 34
visits member for 4 years, 6 months
seen 1 hour ago
associate professor at Rice University

Apr
21
comment Area between 2 curves with absolute value
MO is not for homework and is intended for questions at the mathematics PhD level and above. I've voted to close.
Apr
12
comment Eilenberg-MacLane Spaces of “large” groups
These are more natural things to consider than the comments seem to indicate. For a reasonable topological group $G$, the space $BG$ classifies principal $G$-bundles, while the space $BG^{\delta}$ classifies flat principal $G$-bundles (here $G^{\delta}$ is $G$ considered as a discrete group). So the cohomology of $BG^{\delta}$ consists of characteristic classes for flat bundles; obviously these of great interest.
Apr
12
comment Eilenberg-MacLane Spaces of “large” groups
The conjecture in this paper has recently been proved in most cases by F. Morel; see Corollary 2 of mathematik.uni-muenchen.de/~morel/FriedlanderMilnorNew.pdf
Apr
7
answered On trivalent spines of surfaces
Apr
2
comment Are the mapping class groups of manifolds finitely presentable?
@DannyRuberman : Cool, I didn't know about that paper. Thanks!
Mar
29
awarded  Enlightened
Mar
29
awarded  Nice Answer
Mar
29
comment Are the mapping class groups of manifolds finitely presentable?
Nothing is known in dimension $4$. In dimension $3$, they are always finitely presentable. This is very explicit for prime $3$-manifolds. For instance, the mapping class groups of hyperbolic $3$-manifolds are finite by Mostow rigidity, and one can show that the mapping class groups of Seifert fibered spaces are closely connected to the mapping class groups of their base surfaces. For non-prime $3$-manifolds, things are a little more complicated. Hatcher's survey mentioned in my answer has a good description of all of this.
Mar
29
revised Are the mapping class groups of manifolds finitely presentable?
added 745 characters in body
Mar
29
answered Are the mapping class groups of manifolds finitely presentable?
Mar
25
answered kernel of monodromy action of braid group on homology of hyperelliptic curve
Mar
14
comment References about 3-manifolds
A lesser known source is Fomenko-Matveev's book "Algorithmic and computer methods for three-manifolds". Despite its title, it has nothing to do with computers, but instead is a very nice basic course on 3-manifold topology. The pictures in it are really wonderful.
Mar
4
comment Does the centroid depend continuously on the curve?
@LiviuNicolaescu : I think that Paul is thinking of $\gamma$ as a map from $[0,1]$ to $\mathbb{R}^n$.
Feb
24
comment Modifying Dehn's algorithm to allow equal length replacements?
Remark : A group $G$ has a presentation for which there is a classical Dehn algorithm if and only if $G$ is hyperbolic. You indicated that you know the "if" direction; for the "only if" direction, it is clear that if there is a presentation where the classical Dehn algorithm works, then the group has a linear Dehn function (which is known to be equivalent to hyperbolicity).
Feb
20
comment How do you prove that a subset of L is regular is L is regular?
MO is intended for topics at the mathematics PhD student level and above. I have voted to close.
Feb
20
answered (Un)distorted subgroups in the mapping class group: reference required.
Feb
18
comment Natural constructions (not depending on parameters)
I think that Pete's comment describes the issues with this question perfectly. And I'm sorry if you feel like we demand patience here, but that is the generally agreed upon policy. If you don't get a good answer on math.se, you should think about how to improve your question to get one rather than just copying it here.
Feb
18
comment Natural constructions (not depending on parameters)
I'm not sure this is an appropriate question for MO, but even if it is you only waited 24 hours to get an answer on math.SE. You should wait at least a couple of weeks.
Feb
17
comment Singular chains generated by manifolds with corners — does it really work?
I think I spoke too fast when I wrote that one can following the usual proof word-for-word; I had quickly gone through it and didn't see any obstructions, but you're right that it's not so clear. But if it's true, then surely that's the way to go about proving it.
Feb
16
comment Singular chains generated by manifolds with corners — does it really work?
ps : I'm answering in the comments not because I think this is not a good question (it is!), but because I don't have time right now to write up a detailed answer.