49 research outputs found
Collapsibility to a subcomplex of a given dimension is NP-complete
In this paper we extend the works of Tancer and of Malgouyres and Franc\'es,
showing that -collapsibility is NP-complete for except
. By -collapsibility we mean the following problem: determine
whether a given -dimensional simplicial complex can be collapsed to some
-dimensional subcomplex. The question of establishing the complexity status
of -collapsibility was asked by Tancer, who proved NP-completeness of
and -collapsibility (for ). Our extended result,
together with the known polynomial-time algorithms for and ,
answers the question completely
Leibniz International Proceedings in Information, LIPIcs
We prove that for every d ≥ 2, deciding if a pure, d-dimensional, simplicial complex is shellable is NP-hard, hence NP-complete. This resolves a question raised, e.g., by Danaraj and Klee in 1978. Our reduction also yields that for every d ≥ 2 and k ≥ 0, deciding if a pure, d-dimensional, simplicial complex is k-decomposable is NP-hard. For d ≥ 3, both problems remain NP-hard when restricted to contractible pure d-dimensional complexes
Parametrized Complexity of Expansion Height
Deciding whether two simplicial complexes are homotopy equivalent is a fundamental problem in topology, which is famously undecidable. There exists a combinatorial refinement of this concept, called simple-homotopy equivalence: two simplicial complexes are of the same simple-homotopy type if they can be transformed into each other by a sequence of two basic homotopy equivalences, an elementary collapse and its inverse, an elementary expansion. In this article we consider the following related problem: given a 2-dimensional simplicial complex, is there a simple-homotopy equivalence to a 1-dimensional simplicial complex using at most p expansions? We show that the problem, which we call the erasability expansion height, is W[P]-complete in the natural parameter p
Shellability is NP-Complete
We prove that for every d >= 2, deciding if a pure, d-dimensional, simplicial complex is shellable is NP-hard, hence NP-complete. This resolves a question raised, e.g., by Danaraj and Klee in 1978. Our reduction also yields that for every d >= 2 and k >= 0, deciding if a pure, d-dimensional, simplicial complex is k-decomposable is NP-hard. For d >= 3, both problems remain NP-hard when restricted to contractible pure d-dimensional complexes
Hardness of Approximation for Morse Matching
Discrete Morse theory has emerged as a powerful tool for a wide range of
problems, including the computation of (persistent) homology. In this context,
discrete Morse theory is used to reduce the problem of computing a topological
invariant of an input simplicial complex to computing the same topological
invariant of a (significantly smaller) collapsed cell or chain complex.
Consequently, devising methods for obtaining gradient vector fields on
complexes to reduce the size of the problem instance has become an emerging
theme over the last decade. While computing the optimal gradient vector field
on a simplicial complex is NP-hard, several heuristics have been observed to
compute near-optimal gradient vector fields on a wide variety of datasets.
Understanding the theoretical limits of these strategies is therefore a
fundamental problem in computational topology. In this paper, we consider the
approximability of maximization and minimization variants of the Morse matching
problem, posed as open problems by Joswig and Pfetsch. We establish hardness
results for Max-Morse matching and Min-Morse matching. In particular, we show
that, for a simplicial complex with n simplices and dimension , it is
NP-hard to approximate Min-Morse matching within a factor of
, for any . Moreover, using an L-reduction
from Degree 3 Max-Acyclic Subgraph to Max-Morse matching, we show that it is
both NP-hard and UGC-hard to approximate Max-Morse matching for simplicial
complexes of dimension within certain explicit constant factors.Comment: 20 pages, 1 figur
Discrete Morse theory for the collapsibility of supremum sections
The Dushnik-Miller dimension of a poset is the minimal number of
linear extensions of such that is the
intersection of . Supremum sections are simplicial
complexes introduced by Scarf and are linked to the Dushnik-Miller as follows:
the inclusion poset of a simplicial complex is of Dushnik-Miller dimension at
most if and only if it is included in a supremum section coming from a
representation of dimension . Collapsibility is a topoligical property of
simplicial complexes which has been introduced by Whitehead and which resembles
to shellability. While Ossona de Mendez proved in that a particular type of
supremum sections are shellable, we show in this article that supremum sections
are in general collapsible thanks to the discrete Morse theory developped by
Forman