以下の通り，第4回研究会を開催いたしました．
日時: 2019年9月9日 (月) 16:45～18:00
場所: 京都大学 数理解析研究所 (RIMS) 1階 110室
参加者: 16名
講演者: 平井 広志 氏（東京大学 大学院情報理工学系研究科）
題目: Combinatorial and algorithmic aspects of CAT(0) complexes
概要: A CAT(0) space is a geodesic metric space having globally nonpositive curvature. In this talk, we discuss combinatorial and algorithmic aspects of CAT(0) spacesassociated with combinatorial objects (graphs, posets, etc), from applied mathematics points of view. Topics include:
(1) The space of phylogenetic trees (Billera, Holmes, Vogtmann 2001), and Owen-Provan algorithm (Owen, Provan 2011) computing the geodesic between two phylogenetic trees, via parametric network flow.
(2) Orthoscheme complexes associated with posets (Brady-McCammond 2010), classes of lattices/semilattices having CAT(0) orthoscheme complexes, and their application to submodular optimization.