Seminars in November 2013

  • Hermanshu Kaul, Finding Large induced subgraphs and allocation of resources under dependeny

    Finding Large induced subgraphs and allocation of resources under dependeny
    Hermanshu Kaul
    Illinois Institute of Technology
    2013/11/20 Wednesday 4PM-5PM
    Room 1409

    Given a graph, we are interested in studying the problem of finding an induced subgraph of a fixed order with largest number of edges. More generally, let G = (V, E) be an undirected graph, with a weight (budget) function on the vertices, w: V → ℤ+, and a benefit function on vertices and edges b: EV → ℤ. The benefit of a subgraph H =(VH,EH) is b(H) = ∑ v∈VH b(v) + ∑ e∈EH b(e) while its weight is w(H) = ∑ v∈VH w(v). What can be said about the maximum benefit of an induced subgraph with the restriction that its weight is less than W?

    This problem is closely related to the Quadratic Knapsack Problem, the Densest Subgraph Problem, and classical problems in Extremal Graph Theory. We will discuss these connections, give applications in resource allocation, and present new results on approximation algorithms using methods from convex optimization and probability. This is joint work with Kapoor.

  • Suyoung Choi (최수영), The rational Betti number of small covers and its combinatorics

    The rational Betti number of small covers and its combinatorics
    Suyoung Choi (최수영)
    Department of Mathematics, Ajou University
    2013/11/13 Wednesday 4PM-5PM
    ROOM 1409

    A small cover is a topological analogue of real toric varieties, and is an important object in toric topology. It is noted that the formula of the ℤ2-cohomology ring of small cover is well-known. However, the integral cohomology ring of small covers has not been known well.

    In this talk, we discuss about the Betti numbers and its torsion of the small covers associated to some nestohedra including graph associahedra. Interestingly, the Betti numbers can be computed by purely combinatorial method (in terms of graphs and hypergraphs). To our surprise, for specific families of graphs, these numbers are deeply related to well-known combinatorial sequences such as the Catalan numbers and Euler zigzag numbers.

    Tags:
  • Yoshio Okamoto, Geometric weight balancing

    Geometric weight balancing
    Yoshio Okamoto
    Department of Communication Engineering and Informatics, UEC, Japan
    2013/11/05 Tuesday 11AM – 12AM
    Given a simple polygon P, a point t in P, and a set of positive weights, we want to place the weights on the boundary of P in such a way that their barycenter comes to t. We show that there is always such a placement if the weights are balanced, i.e., no weight is larger than half of the total weight, and the placement can be found efficiently. We also study three-dimensional versions of the problem.</p>

    Joint work with Luis Barba, Jean Lou De Carufel, Rudolf Fleischer, Akitoshi Kawamura, Matias Korman, Yuan Tang, Takeshi Tokuyama, Sander Verdonschot, and Tianhao Wang.

Monthly Archives