Gregory Clark

 Gregory Clark

Gregory J. Clark

  • Courses10
  • Reviews25

Biography

University of South Carolina - Mathematics

PHD Graduate Student at University of South Carolina
Gregory
Clark
Columbia, South Carolina Area
My research is in discrete mathematics; specifically, spectral hypergraph theory, computational algebra, crossing numbers, and network modeling. A central theme of my dissertation work is exploring the characteristic polynomial of a hypergraph which is connected to numerous fields of mathematics because this polynomial is the resultant of a system of multilinear homogeneous equations. The resultant, which is a generalization of the determinant, is central to algebraic geometry, commutative algebra, and numerical multilinear algebra among other areas. My dissertation gives a generalization of the Harary-Sachs Theorem by providing a combinatorial description of the coefficients of characteristic polynomial of a hypergraph. This result is valuable because we can compute the leading coefficients of this particular polynomial without needing to compute all the coefficients, which is NP-hard to compute in general. Furthermore, I have provided a numerically stable algorithm which can compute the characteristic polynomial of a hypergraph given its set spectrum and leading coefficients. This allows for the computation of the characteristic polynomial of a hypergraph when traditional tools from commutative algebra (i.e., the resultant) have been insufficient. In addition to my dissertation work I have also collaborated on the study of crossing number problems and have applied my research in hypergraphs to the study of online black markets.

Education

  • University of South Carolina

    Doctor of Philosophy - PhD

    Mathematics

Publications

  • Optimal Numbers and Solutions in the Euclidean Algorithm

    The Pentagon, A Mathematics Magazine for Students

  • Optimal Numbers and Solutions in the Euclidean Algorithm

    The Pentagon, A Mathematics Magazine for Students

  • Tiling Annular Regions with Skew and T-tetrominoes

    Involve, a Journal of Mathematics

    In this paper, we study tilings of annular regions in the integer lattice by skew and T-tetrominoes. We demonstrate the tileability of most annular regions by the given tile set, enumerate the tilings of width-2 annuli, and determine the tile counting group associated to this tile set and the family of all width-2 annuli.

  • Optimal Numbers and Solutions in the Euclidean Algorithm

    The Pentagon, A Mathematics Magazine for Students

  • Tiling Annular Regions with Skew and T-tetrominoes

    Involve, a Journal of Mathematics

    In this paper, we study tilings of annular regions in the integer lattice by skew and T-tetrominoes. We demonstrate the tileability of most annular regions by the given tile set, enumerate the tilings of width-2 annuli, and determine the tile counting group associated to this tile set and the family of all width-2 annuli.

  • Leading Coefficients and the Multiplicity of Known Roots

    Submitted.

    We show that a monic univariate polynomial over a field of characteristic zero, with k distinct non-zero known roots, is determined by its k proper leading coefficients by providing an explicit algorithm for computing the multiplicities of each root. We provide a version of the result and accompanying algorithm when the field is not algebraically closed by considering the minimal polynomials of the roots. Furthermore, we show how to perform the aforementioned algorithm in a numerically stable manner over ℂ, and then apply it to obtain new characteristic polynomials of hypergraphs.

  • Optimal Numbers and Solutions in the Euclidean Algorithm

    The Pentagon, A Mathematics Magazine for Students

  • Tiling Annular Regions with Skew and T-tetrominoes

    Involve, a Journal of Mathematics

    In this paper, we study tilings of annular regions in the integer lattice by skew and T-tetrominoes. We demonstrate the tileability of most annular regions by the given tile set, enumerate the tilings of width-2 annuli, and determine the tile counting group associated to this tile set and the family of all width-2 annuli.

  • Leading Coefficients and the Multiplicity of Known Roots

    Submitted.

    We show that a monic univariate polynomial over a field of characteristic zero, with k distinct non-zero known roots, is determined by its k proper leading coefficients by providing an explicit algorithm for computing the multiplicities of each root. We provide a version of the result and accompanying algorithm when the field is not algebraically closed by considering the minimal polynomials of the roots. Furthermore, we show how to perform the aforementioned algorithm in a numerically stable manner over ℂ, and then apply it to obtain new characteristic polynomials of hypergraphs.

  • Using Block Designs in Crossing Number Bounds

    Journal of Combinatorial Designs

    The crossing number cr(G) of a graph G=(V,E) is the smallest number of edge crossings over all drawings of G in the plane. For any k≥1, the k-planar crossing number of G, cr_k(G), is defined as the minimum of cr(G_1)+cr(G_2)+…+cr(G_k) over all graphs G_1,G_2,…,G_k whose union is G. Pach et al. showed that for every k≥1, we have cr_k(G)≤(2/k^2−1/k^3)cr(G) and that this bound does not remain true if we replace the constant 2/k^2−1/k^3 by any number smaller than 1/k^2. We improve the upper bound to 1/k^2(1+o(1)) as k→∞. For the class of bipartite graphs, we show that the best constant is exactly 1/k^2 for every k. The results extend to the rectilinear variant of the k-planar crossing number. To appear.

  • Optimal Numbers and Solutions in the Euclidean Algorithm

    The Pentagon, A Mathematics Magazine for Students

  • Tiling Annular Regions with Skew and T-tetrominoes

    Involve, a Journal of Mathematics

    In this paper, we study tilings of annular regions in the integer lattice by skew and T-tetrominoes. We demonstrate the tileability of most annular regions by the given tile set, enumerate the tilings of width-2 annuli, and determine the tile counting group associated to this tile set and the family of all width-2 annuli.

  • Leading Coefficients and the Multiplicity of Known Roots

    Submitted.

    We show that a monic univariate polynomial over a field of characteristic zero, with k distinct non-zero known roots, is determined by its k proper leading coefficients by providing an explicit algorithm for computing the multiplicities of each root. We provide a version of the result and accompanying algorithm when the field is not algebraically closed by considering the minimal polynomials of the roots. Furthermore, we show how to perform the aforementioned algorithm in a numerically stable manner over ℂ, and then apply it to obtain new characteristic polynomials of hypergraphs.

  • Using Block Designs in Crossing Number Bounds

    Journal of Combinatorial Designs

    The crossing number cr(G) of a graph G=(V,E) is the smallest number of edge crossings over all drawings of G in the plane. For any k≥1, the k-planar crossing number of G, cr_k(G), is defined as the minimum of cr(G_1)+cr(G_2)+…+cr(G_k) over all graphs G_1,G_2,…,G_k whose union is G. Pach et al. showed that for every k≥1, we have cr_k(G)≤(2/k^2−1/k^3)cr(G) and that this bound does not remain true if we replace the constant 2/k^2−1/k^3 by any number smaller than 1/k^2. We improve the upper bound to 1/k^2(1+o(1)) as k→∞. For the class of bipartite graphs, we show that the best constant is exactly 1/k^2 for every k. The results extend to the rectilinear variant of the k-planar crossing number. To appear.

  • On the Adjacency Spectra of Hypertrees

    The Electronic Journal of Combinatorics

    We extend the results of Zhang et al. to show that λ is an eigenvalue of a k-uniform hypertree (k≥3) if and only if it is a root of a particular matching polynomial for a connected induced subtree. We then use this to provide a spectral characterization for power hypertrees. Notably, the situation is quite different from that of ordinary trees, i.e., 2-uniform trees. We conclude by presenting an example (an 11 vertex, 3-uniform non-power hypertree) illustrating these phenomena.

  • Optimal Numbers and Solutions in the Euclidean Algorithm

    The Pentagon, A Mathematics Magazine for Students

  • Tiling Annular Regions with Skew and T-tetrominoes

    Involve, a Journal of Mathematics

    In this paper, we study tilings of annular regions in the integer lattice by skew and T-tetrominoes. We demonstrate the tileability of most annular regions by the given tile set, enumerate the tilings of width-2 annuli, and determine the tile counting group associated to this tile set and the family of all width-2 annuli.

  • Leading Coefficients and the Multiplicity of Known Roots

    Submitted.

    We show that a monic univariate polynomial over a field of characteristic zero, with k distinct non-zero known roots, is determined by its k proper leading coefficients by providing an explicit algorithm for computing the multiplicities of each root. We provide a version of the result and accompanying algorithm when the field is not algebraically closed by considering the minimal polynomials of the roots. Furthermore, we show how to perform the aforementioned algorithm in a numerically stable manner over ℂ, and then apply it to obtain new characteristic polynomials of hypergraphs.

  • Using Block Designs in Crossing Number Bounds

    Journal of Combinatorial Designs

    The crossing number cr(G) of a graph G=(V,E) is the smallest number of edge crossings over all drawings of G in the plane. For any k≥1, the k-planar crossing number of G, cr_k(G), is defined as the minimum of cr(G_1)+cr(G_2)+…+cr(G_k) over all graphs G_1,G_2,…,G_k whose union is G. Pach et al. showed that for every k≥1, we have cr_k(G)≤(2/k^2−1/k^3)cr(G) and that this bound does not remain true if we replace the constant 2/k^2−1/k^3 by any number smaller than 1/k^2. We improve the upper bound to 1/k^2(1+o(1)) as k→∞. For the class of bipartite graphs, we show that the best constant is exactly 1/k^2 for every k. The results extend to the rectilinear variant of the k-planar crossing number. To appear.

  • On the Adjacency Spectra of Hypertrees

    The Electronic Journal of Combinatorics

    We extend the results of Zhang et al. to show that λ is an eigenvalue of a k-uniform hypertree (k≥3) if and only if it is a root of a particular matching polynomial for a connected induced subtree. We then use this to provide a spectral characterization for power hypertrees. Notably, the situation is quite different from that of ordinary trees, i.e., 2-uniform trees. We conclude by presenting an example (an 11 vertex, 3-uniform non-power hypertree) illustrating these phenomena.

  • New Bounds on the Biplanar Crossing Number of Low-dimensional Hypercubes

    Bulletin of the Institute of Combinatorics and its Applications (BICA)

    In this note we provide an improved upper bound on the biplanar crossing number of the 8-dimensional hypercube. The k-planar crossing number of a graph crk(G) is the number of crossings required when every edge of G must be drawn in one of k distinct planes. It was shown in Czabarka et al. that cr2(Q8)≤256 which we improve to cr2(Q8)≤128. Our approach highlights the relationship between symmetric drawings and the study of k-planar crossing numbers. We conclude with several open questions concerning this relationship.

Possible Matching Profiles

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  • Gregory Clark (00% Match)
    Instructor
    Coast Community College District - Coast Community College District

  • Gregory Clark (00% Match)
    Professor
    University Of California - University Of California

CALCI 141

4.5(1)

CALCULUS 14

4.5(1)

MATH 115

4.3(4)

MATH 122

4.8(5)

MATH 141

4.6(5)

MTH 141

4.3(4)