330 research outputs found
Random Discrete Morse Theory and a New Library of Triangulations
1) We introduce random discrete Morse theory as a computational scheme to
measure the complicatedness of a triangulation. The idea is to try to quantify
the frequence of discrete Morse matchings with a certain number of critical
cells. Our measure will depend on the topology of the space, but also on how
nicely the space is triangulated.
(2) The scheme we propose looks for optimal discrete Morse functions with an
elementary random heuristic. Despite its na\"ivet\'e, this approach turns out
to be very successful even in the case of huge inputs.
(3) In our view the existing libraries of examples in computational topology
are `too easy' for testing algorithms based on discrete Morse theory. We
propose a new library containing more complicated (and thus more meaningful)
test examples.Comment: 35 pages, 5 figures, 7 table
Computational Geometric and Algebraic Topology
Computational topology is a young, emerging field of mathematics that seeks out practical algorithmic methods for solving complex and fundamental problems in geometry and topology. It draws on a wide variety of techniques from across pure mathematics (including topology, differential geometry, combinatorics, algebra, and discrete geometry), as well as applied mathematics and theoretical computer science. In turn, solutions to these problems have a wide-ranging impact: already they have enabled significant progress in the core area of geometric topology, introduced new methods in applied mathematics, and yielded new insights into the role that topology has to play in fundamental problems surrounding computational complexity.
At least three significant branches have emerged in computational topology: algorithmic 3-manifold and knot theory, persistent homology and surfaces and graph embeddings. These branches have emerged largely independently. However, it is clear that they have much to offer each other. The goal of this workshop was to be the first significant step to bring these three areas together, to share ideas in depth, and to pool our expertise in approaching some of the major open problems in the field
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
Chromatic Numbers of Simplicial Manifolds
Higher chromatic numbers of simplicial complexes naturally
generalize the chromatic number of a graph. In any fixed dimension
, the -chromatic number of -complexes can become arbitrarily
large for [6,18]. In contrast, , and only
little is known on for .
A particular class of -complexes are triangulations of -manifolds. As a
consequence of the Map Color Theorem for surfaces [29], the 2-chromatic number
of any fixed surface is finite. However, by combining results from the
literature, we will see that for surfaces becomes arbitrarily large
with growing genus. The proof for this is via Steiner triple systems and is
non-constructive. In particular, up to now, no explicit triangulations of
surfaces with high were known.
We show that orientable surfaces of genus at least 20 and non-orientable
surfaces of genus at least 26 have a 2-chromatic number of at least 4. Via a
projective Steiner triple systems, we construct an explicit triangulation of a
non-orientable surface of genus 2542 and with face vector
that has 2-chromatic number 5 or 6. We also give orientable examples with
2-chromatic numbers 5 and 6.
For 3-dimensional manifolds, an iterated moment curve construction [18] along
with embedding results [6] can be used to produce triangulations with
arbitrarily large 2-chromatic number, but of tremendous size. Via a topological
version of the geometric construction of [18], we obtain a rather small
triangulation of the 3-dimensional sphere with face vector
and 2-chromatic number 5.Comment: 22 pages, 11 figures, revised presentatio
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