Hidefumi Ohsugi

  1. Roots of Ehrhart polynomials of Gorenstein Fano polytopes.

    Authors: Takayuki Hibi, Akihiro Higashitani, Hidefumi Ohsugi
    Subjects: Combinatorics
    Abstract

    Given arbitrary integers $k$ and $d$ with $0 \leq 2k \leq d$, we construct a
    Gorenstein Fano polytope $\Pc \subset \RR^d$ of dimension $d$ such that (i) its
    Ehrhart polynomial $i(\Pc, n)$ possesses $d$ distinct roots; (ii) $i(\Pc, n)$
    possesses exactly $2k$ imaginary roots; (iii) $i(\Pc, n)$ possesses exactly $d
    - 2k$ real roots; (iv) the real part of each of the imaginary roots is equal to
    $- 1 / 2$; (v) all of the real roots belong to the open interval $(-1, 0)$.

  2. Non-very ample configurations arising from contingency tables.

    Authors: Takayuki Hibi, Hidefumi Ohsugi
    Subjects: Commutative Algebra
    Abstract

    In this paper, it is proved that, if a toric ideal possesses a fundamental
    binomial none of whose monomials is squarefree, then the corresponding
    semigroup ring is not very ample. Moreover, very ample semigroup rings of
    Lawrence type are discussed. As an application, we study very ampleness of
    configurations arising from contingency tables.

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