Annotating simplices with a homology basis and its applications Technical Article

Author(s): Busaryev, Oleksiy; Cabello, Sergio; Chen, Chao; Dey, Tamal K; Wang, Yusu
Title: Annotating simplices with a homology basis and its applications
Affiliation IST Austria
Abstract: Let K be a simplicial complex and g the rank of its p-th homology group Hp(K) defined with Z2 coefficients. We show that we can compute a basis H of Hp(K) and annotate each p-simplex of K with a binary vector of length g with the following property: the annotations, summed over all p-simplices in any p-cycle z, provide the coordinate vector of the homology class [z] in the basis H. The basis and the annotations for all simplices can be computed in O(nω) time, where n is the size of K and ω<2.376 is a quantity so that two n×n matrices can be multiplied in O(nω) time. The pre-computation of annotations permits answering queries about the independence or the triviality of p-cycles efficiently. Using annotations of edges in 2-complexes, we derive better algorithms for computing optimal basis and optimal homologous cycles in 1-dimensional homology. Specifically, for computing an optimal basis of H1(K), we improve the time complexity known for the problem from O(n4) to O(nω+n2gω−1). Here n denotes the size of the 2-skeleton of K and g the rank of H1(K). Computing an optimal cycle homologous to a given 1-cycle is NP-hard even for surfaces and an algorithm taking 2O(g)nlogn time is known for surfaces. We extend this algorithm to work with arbitrary 2-complexes in O(nω)+2O(g)n2logn time using annotations.
Publication Title: CoRR: Computing Research Repository
Issue abs/1107.3793
Publisher: ArXiv  
Date Published: 2011-07-19
Open access: yes (repository)
IST Austria Authors
  1. Chao Chen
    14 Chen
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