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Homotopy theory, homological algebra, algebraic treatments of manifolds.

78 votes
1 answer
5k views

The topology of Arithmetic Progressions of primes

The primary motivation for this question is the following: I would like to extract some topological statistics which capture how arithmetic progressions of prime numbers "fit together" in a manner tha …
Vidit Nanda's user avatar
  • 15.5k
47 votes
6 answers
5k views

Can we actually find any fixed points with Brouwer's theorem?

Background At the risk of greatly oversimplifying matters, let me state a heuristic from Granas and Dugundji's beautiful book: fixed point theorems fall into two broad categories. The first class is …
Vidit Nanda's user avatar
  • 15.5k
37 votes
Accepted

Reference on Persistent Homology

Since this area is developing rather quickly, there is a dearth of canonical references that would satisfy basic pedagogical requirements. If I were teaching a course on this material right now, I wou …
Vidit Nanda's user avatar
  • 15.5k
29 votes

An "advanced beginner's" book on algebraic topology?

It is somewhat jarring to hear of people who "know nothing about the homology theories of topological spaces and their applications" but are "familiar with homological algebra, category theory, spectr …
28 votes
1 answer
1k views

Is there a general theory of fiber theorems?

Here are three vague theorems rolled up in one. Let $X$ and $Y$ be sufficiently nice topological spaces and $f:X \to Y$ a sufficiently nice surjection. If for each $y \in Y$, the fiber $f^{-1}(y) …
Vidit Nanda's user avatar
  • 15.5k
27 votes
Accepted

Inference using Topological Data Analysis: Is it worth it for a regular statistician to lear...

Let me answer the broad question first: depending on what you actually want to do, the barcode-type invariants extracted by topological data analysis could be quite useful in your work. And it doesn't …
Vidit Nanda's user avatar
  • 15.5k
24 votes
4 answers
2k views

How many simplicial complexes on n vertices up to homotopy equivalence?

Fix a number $n$, and define $\gamma(n)$ to be the number of simplicial complexes on $n$ unlabeled vertices up to homotopy equivalence. It is unlikely that an explicit formula exists, but what is know …
Vidit Nanda's user avatar
  • 15.5k
22 votes
Accepted

fixed point property for maps of compacts

Lovely question! Sadly, the answer is "no" in the sense that the fixed point property is not homotopy-invariant even in the category of finite polyhedra. In fact, it is also not invariant under the op …
Vidit Nanda's user avatar
  • 15.5k
22 votes
0 answers
3k views

Origins of the Nerve Theorem

Recently, I've read two papers which have cited the Nerve Theorem, one crediting Borsuk with the result and another Leray. Here is the question: Who was the first to prove the Nerve Theorem?
Vidit Nanda's user avatar
  • 15.5k
22 votes
0 answers
668 views

Are there "chain complexes" and "homology groups" taking values in pairs of topological spaces?

Throughout this question, notation of the form $(X,A)$ denotes a sufficiently nice pair of topological spaces. I think for most of what I'm saying here, it is enough to assume that the inclusion $A \h …
Vidit Nanda's user avatar
  • 15.5k
18 votes
Accepted

Persistence barcodes and spectral sequences

The answer to your question is no, nobody has used persistence to improve the algorithmic efficiency of computing differentials, although of course the relationship between persistence intervals of a …
Vidit Nanda's user avatar
  • 15.5k
16 votes
1 answer
359 views

Moduli space of boundary maps with prescribed chain and homology groups?

Let $R$ be a reasonable ring (maybe I mean a PID, or $\mathbb{Z}$, and when sufficiently desperate, a field). Now consider fixed sequences $C_n$ and $H_n$ of $R$-modules, which are tame in every possi …
Vidit Nanda's user avatar
  • 15.5k
12 votes

Inference using Topological Data Analysis: Is it worth it for a regular statistician to lear...

Update: There is a now a new paper by Otter et al which went through all the trouble of comparing many software packages for performance, memory, ease-of-use etc.: http://arxiv.org/abs/1506.08903 Thi …
Vidit Nanda's user avatar
  • 15.5k
11 votes
0 answers
202 views

Fundamental groups of reduced subgroup lattices

Let $G$ be a group. Its subgroup lattice, denoted $\Sigma G$, consists of all subgroups of $G$ partially ordered by inclusion. The topology of this poset is quite trivial, since it always has a maxima …
Vidit Nanda's user avatar
  • 15.5k
11 votes

Computer-aided homology computations

I realize that this is an old question and it is likely that the OP has moved on, but let me summarize the state-of-the-art as it exists now. The given sizes (18 million by 15 million) are pretty h …
Vidit Nanda's user avatar
  • 15.5k

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