Cubical abelian groups with connections are equivalent to chain complexes

Cubical Ripser: Software for computing persistent homology of image and volume data

We introduce Cubical Ripser for computing persistent homology of image and volume data (more precisely, weighted cubical complexes). To our best knowledge, Cubical Ripser is currently the fastest and the most memory-efficient program for computing persistent homology of weighted cubical complexes. We demonstrate our software with an example of image analysis in which persistent homology and convolutional neural networks are successfully combined. Our open-source implementation is available online.

Topology of random 2-dimensional cubical complexes

We study a natural model of random 2-dimensional cubical complex which is a subcomplex of an n-dimensional cube, and where every possible square $2$-face is included independently with probability p. Our main result is to exhibit a sharp threshold p=1/2 for homology vanishing as $n \to \infty$. This is a 2-dimensional analogue of the Burtin and Erdős-Spencer theorems characterizing the connectivity threshold for random cubical graphs. Our main result can also be seen as a cubical counterpart to the Linial--Meshulam theorem for random 2-dimensional simplicial complexes. However, the models exhi…

双数字图像构造的持续同调

The Persistent Homology of Dual Digital Image Constructions

研究灰度数字图像的两种立方复形构造的持续同调差异，通过对偶滤过胞腔复形理论推导出转换方法，使软件无需额外低级代码即可支持两种构造。

Homotopy Types of Random Cubical Complexes

We study the topology of a random cubical complex associated to Bernoulli site percolation on a cubical grid. We begin by establishing a limit law for homotopy types. More precisely, looking within an expanding window, we define a sequence of normalized counting measures (counting connected components according to homotopy type), and we show that this sequence of random probability measures converges in probability to a deterministic probability measure. We then investigate the dependence of the limiting homotopy measure on the coloring probability $p$, and our results show a qualitative chang…

Polytopal complexes: maps, chain complexes and... necklaces

The notion of polytopal map between two polytopal complexes is defined. Surprisingly, this definition is quite simple and extends naturally those of simplicial and cubical maps. It is then possible to define an induced chain map between the associated chain complexes. Finally, we use this new tool to give the first combinatorial proof of the splitting necklace theorem of Alon. The paper ends with open questions, such as the existence of Sperner's lemma for a polytopal complex or the existence of a cubical approximation theorem.

离散同伦理论的立方设定再探

Cubical setting for discrete homotopy theory, revisited

本文提出了一种将图转换为Kan复杂性的立方集构造方法，并证明了图的A群与同伦群的关系，同时验证了一个长期猜想并加强了Hurewicz定理的证明。

Crossed complexes and homotopy groupoids as non commutative tools for higher dimensional local-to-global problems

We outline the main features of the definitions and applications of crossed complexes and cubical $ω$-groupoids with connections. These give forms of higher homotopy groupoids, and new views of basic algebraic topology and the cohomology of groups, with the ability to obtain some non commutative results and compute some homotopy types.

On the Cubical Homology Groups of Free Partially Commutative Monoids

We study a Leech homology of a locally bounded free partially commutative monoid $M(E,I)$. Given a contravariant natural system of abelian groups $F$ on $M(E,I)$ we build a precubical set $T(E,I)$ with a homological system of abelian groups $\bar{F}$ and prove that the Leech homology groups $H_n(M(E,I),F)$ are isomorphic to the cubical homology groups $H_n(T(E,I),\bar{F})$, $n\geq 0$. As a consequence we have confirmed a conjecture that if the free partially commutative monoid does not contain $>n$ mutually commuting generators, then its the homological dimension $\leq n$. We have built the co…

Moment-angle complexes and combinatorics of simplicial manifolds

Let $ρ:(D^2)^m\to I^m$ be the orbit map for the diagonal action of the torus $T^m$ on the unit poly-disk $(D^2)^m$, $I^m=[0,1]^m$ is the unit cube. Let $C$ be a cubical subcomplex in $I^m$. The moment-angle complex $\ma(C)$ is a $T^m$-invariant bigraded cellular decomposition of the subset $ρ^{-1}(C)\subset(D^2)^m$ with cells corresponding to the faces of $C$. Different combinatorial problems concerning cubical complexes and related combinatorial objects can be treated by studying the equivariant topology of corresponding moment-angle complexes. Here we consider moment-angle complexes defined …

A metric Kan-Thurston theorem

For every simplicial complex X, we construct a locally CAT(0) cubical complex T_X, a cellular isometric involution i on T_X and a map t_X from T_X to X with the following properties: t_Xi = t_X; t_X is a homology isomorphism; the induced map from the quotient of T_X by the involution i to X is a homotopy equivalence; the induced map from the fixed point subspace for i in T_X to X is a homology isomorphism. The construction is functorial in X. One corollary is an equivariant Kan-Thurston theorem: every connected proper G-CW-complex has the same equivariant homology as the classifying space for …

紧度量空间上不可嵌入立方平移的等距自由Z-作用

A free Z-action by isometries on a compact metric space which is not embeddable into a cubical shift

本文构造了一个紧度量空间上的等距自由Z-作用，证明其不可嵌入立方平移，从而以存在性定理的形式强力回答了拓扑动力学中的一个著名公开问题，核心工具是Borsuk-Ulam型定理、p进完备化与等变Sullivan猜想。

Isomorphism of the cubical and categorical cohomology groups of a higher-rank graph

We use category-theoretic techniques to provide two proofs showing that for a higher-rank graph $Λ$, its cubical (co-)homology and categorical (co-)homology groups are isomorphic in all degrees, thus answering a question of Kumjian, Pask and Sims in the positive. Our first proof uses the topological realization of a higher-rank graph, which was introduced by Kaliszewski, Kumjian, Quigg, and Sims. In our more combinatorial second proof, we construct, explicitly and in both directions, maps on the level of (co-)chain complexes that implement said isomorphism. Along the way, we extend the definit…

Multisimplicial chains and configuration spaces

This paper presents a generalization to multisimplicial sets of previously defined $E_\infty$-coalgebra structures on the chains of simplicial and cubical sets. We focus on the surjection chain complexes of McClure--Smith as a main example and construct a zig-zag of complexity preserving quasi-isomorphisms of $E_\infty$-coalgebras relating these to both the singular chains on configuration spaces and the Barratt--Eccles chain complexes.

Torus actions, combinatorial topology and homological algebra

The paper surveys some new results and open problems connected with such fundamental combinatorial concepts as polytopes, simplicial complexes, cubical complexes, and subspace arrangements. Particular attention is paid to the case of simplicial and cubical subdivisions of manifolds and, especially, spheres. We describe important constructions which allow to study all these combinatorial objects by means of methods of commutative and homological algebra. The proposed approach to combinatorial problems relies on the theory of moment-angle complexes, currently being developed by the authors. The …

Cohomology of colorings of cycles

We compute the cohomology groups of the spaces of colorings of cycles, i.e., of the prodsimplicial complexes Hom(C_m,K_n). We perform the computation first with Z_2, and then with integer coefficients. The main technical tool is to use spectral sequences in conjunction with a detailed combinatorial analysis of a family of cubical complexes, which we call torus front complexes. As an application of our method, we demonstrate how to collapse each connected component of Hom(C_m,C_n) onto a garland of cubes.

从帧到特征：面向二值视频的可缩放之字形持续同调

From Frames to Features: Scalable Zigzag Persistence for Binary Video

提出一种直接从连通分量动力学提取H0和H1条形码的方法，通过图编码避免立方复形构造，利用Dey-Hou近线性时间算法实现4k视频实时分析。

Homomorphism Complexes and Maximal Chains in Graded Posets

We apply the homomorphism complex construction to partially ordered sets, introducing a new topological construction based on the set of maximal chains in a graded poset. Our primary objects of study are distributive lattices, with special emphasis on finite products of chains. For the special case of a Boolean algebra, we observe that the corresponding homomorphism complex is isomorphic to the subcomplex of cubical cells in a permutahedron. Thus, this work can be interpreted as a generalization of the study of these complexes. We provide a detailed investigation when our poset is a product of…

Brown representability often fails for homotopy categories of complexes

We show that for the homotopy category K(Ab) of complexes of abelian groups, both Brown representability and Brown representability for the dual fail. We also provide an example of a localizing subcategory of K(Ab) for which the inclusion into K(Ab) does not have a right adjoint.

Dold-Kan correspondence for dendroidal abelian groups

We prove a Dold-Kan type correspondence between the category of dendroidal abelian groups and a suitably constructed category of dendroidal complexes. Our result naturally extends the classical Dold-Kan correspondence between the category of simplicial abelian groups and the category of non-negatively graded chain complexes.

The model structure for chain complexes

Let $\text{Ch}$ be the category of (possibly unbounded) chain complexes of abelian groups. In this note we construct the standard Quillen model structure on $\text{Ch}$, by a method that is somewhat different from the standard one. Essentially, we use a functorial two-stage projective resolution for abelian groups, and build everything directly from that. This has the advantage of being very concrete, explicit and functorial. It does not rely on the small object argument, or make any explicit use of transfinite induction. On the other hand, it is not so conceptual, and it does use the fact tha…

K-flat complexes and derived categories

Let $R$ be a ring with identity. Inspired by recent work of Emmanouil, we show that the derived category of $R$ is equivalent to the chain homotopy category of all K-flat complexes with pure-injective components. This is implicitly related to a recollement we exhibit. It expresses $\mathcal{D}_{pur}(R)$, the pure derived category of $R$, as an attachment of the usual derived category $\mathcal{D}(R)$ with Emmanouil's quotient category $\mathcal{D}_{K-flat}(R):=K(R)/K-Flat$, which here we call the K-flat derived category. It follows that this Verdier quotient is a compactly generated triangulat…

Vertex numbers of simplicial complexes with free abelian fundamental group

We show that the minimum number of vertices of a simplicial complex with fundamental group $\mathbb{Z}^{n}$ is at most $O(n)$ and at least $Ω(n^{3/4})$. For the upper bound, we use a result on orthogonal 1-factorizations of $K_{2n}$. For the lower bound, we use a fractional Sylvester-Gallai result. We also prove that any group presentation $\langle S | R\rangle \cong \mathbb{Z}^{n}$ whose relations are of the form $g^{a}h^{b}i^{c}$ for $g, h, i \in S$ has at least $Ω(n^{3/2})$ generators.

A realization functor for abelian model categories

We study liftings of abelian model structures to categories of chain complexes and construct a realization functor from the derived category of a Grothendieck abelian category equipped with a cofibrantly generated, hereditary abelian model structure to the homotopy category of that model structure.

Homotopy colimits and global observables in Abelian gauge theory

We study chain complexes of field configurations and observables for Abelian gauge theory on contractible manifolds, and show that they can be extended to non-contractible manifolds by using techniques from homotopy theory. The extension prescription yields functors from a category of manifolds to suitable categories of chain complexes. The extended functors properly describe the global field and observable content of Abelian gauge theory, while the original gauge field configurations and observables on contractible manifolds are recovered up to a natural weak equivalence.

组合复形：弥合胞腔复形与超图之间的鸿沟

Combinatorial Complexes: Bridging the Gap Between Cell Complexes and Hypergraphs

该研究指出超图与胞腔复形分别侧重集合型多体关系和层级式内部-边界关系，提出可融合两类关系的组合复形概念，并通过数值实验验证其在学习任务中的建模优势。

Small simplicial complexes with prescribed torsion in homology

For $d \geq 2$ and $G$ a finite abelian group, define $T_d(G)$ to be the minimum number of vertices $n$ so that there exists a simplicial complex $X$ on $n$ vertices which has the torsion part of $H_{d - 1}(X)$ isomorphic to $G$. Here we establish an upper bound on $T_d(G)$ which matches the known lower bound up to a constant factor. That is, we prove that for every $d \geq 2$ there exist constants $c_d$ and $C_d$ so that for any finite abelian group $c_d(\log |G|)^{1/d} \leq T_d(G) \leq C_d(\log |G|)^{1/d}.$