Benjamin A. Burton

  1. Complementary vertices and adjacency testing in polytopes.

    Authors: Benjamin A. Burton
    Subjects: Combinatorics
    Abstract

    Our main theoretical result is that, if a simple polytope has a pair of
    complementary vertices (i.e., two vertices with no facets in common), then it
    has a second such pair.

  2. Fundamental normal surfaces and the enumeration of Hilbert bases.

    Authors: Benjamin A. Burton
    Subjects: Geometric Topology
    Abstract

    Normal surfaces are a key tool in computational knot theory and 3-manifold
    topology, and have featured in significant computational breakthroughs in
    recent years. Despite this, there has been little practical progress on
    algorithms that use fundamental normal surfaces, which are described in terms
    of a Hilbert basis for a pointed rational cone on a high-dimensional integer
    lattice. In this paper we develop and implement several algorithms to enumerate
    fundamental normal surfaces, by merging domain-specific techniques from normal
    surface theory with classical Hilbert basis algorithms.

  3. Maximal admissible faces and asymptotic bounds for the normal surface solution space.

    Authors: Benjamin A. Burton
    Subjects: Geometric Topology
    Abstract

    The enumeration of normal surfaces is a key bottleneck in computational
    three-dimensional topology. The underlying procedure is the enumeration of
    admissible vertices of a high-dimensional polytope, where admissibility is a
    powerful but non-linear and non-convex constraint.

  4. The complexity of the normal surface solution space.

    Authors: Benjamin A. Burton
    Subjects: Geometric Topology
    Abstract

    Normal surface theory is a central tool in algorithmic three-dimensional
    topology, and the enumeration of vertex normal surfaces is the computational
    bottleneck in many important algorithms. However, it is not well understood how
    the number of such surfaces grows in relation to the size of the underlying
    triangulation. Here we address this problem in both theory and practice. In
    theory, we tighten the exponential upper bound substantially; furthermore, we
    construct pathological triangulations that prove an exponential bound to be
    unavoidable.

  5. Searching a bitstream in linear time for the longest substring of any given density.

    Authors: Benjamin A. Burton
    Subjects: Data Structures and Algorithms
    Abstract

    Given an arbitrary bitstream, we consider the problem of finding the longest
    substring whose ratio of ones to zeroes equals a given value. The central
    result of this paper is an algorithm that solves this problem in linear time.
    The method involves (i) reformulating the problem as a constrained walk through
    a sparse matrix, and then (ii) developing a data structure for this sparse
    matrix that allows us to perform each step of the walk in amortised constant
    time.

  6. The Weber-Seifert dodecahedral space is non-Haken.

    Authors: Benjamin A. Burton, J. Hyam Rubinstein, Stephan Tillmann
    Subjects: Geometric Topology
    Abstract

    In this paper we develop a new test to help identify whether a closed,
    orientable, irreducible 3-manifold is non-Haken. The test builds on work by
    Jaco and Oertel, and also incorporates heuristic pruning techniques to test
    whether a normal surface is compressible. As an application, we settle
    Thurston's old question of whether the Weber-Seifert dodecahedral space is
    non-Haken.

  7. Quadrilateral-octagon coordinates for almost normal surfaces.

    Authors: Benjamin A. Burton
    Subjects: Geometric Topology
    Abstract

    Normal and almost normal surfaces are essential tools for algorithmic
    3-manifold topology, but to use them requires exponentially slow enumeration
    algorithms in a high-dimensional vector space. The quadrilateral coordinates of
    Tollefson alleviate this problem considerably for normal surfaces, by reducing
    the dimension of this vector space from 7n to 3n (where n is the complexity of
    the underlying triangulation). Here we develop an analogous theory for
    octagonal almost normal surfaces, using quadrilateral and octagon coordinates
    to reduce this dimension from 10n to 6n.

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