Department of Computer Science | Institute of Theoretical Computer Science | CADMO

Theory of Combinatorial Algorithms

Prof. Emo Welzl and Prof. Bernd Gärtner

Mittagsseminar (in cooperation with A. Steger, D. Steurer and B. Sudakov)

Mittagsseminar Talk Information

Date and Time: Thursday, May 04, 2023, 12:15 pm

Duration: 30 minutes

Location: CAB G51

Speaker: Hung Hoang (Amazon)

Zigzagging through acyclic orientations of graphs and hypergraphs

In 1993, Savage, Squire, and West described an inductive construction for generating every acyclic orientation of a chordal graph exactly once, flipping one arc at a time. In this talk, I will mention two generalizations of this result. The first is Gray codes for acyclic orientations of hypergraphs that satisfy a simple ordering condition, which generalizes the notion of perfect elimination order of chordal graphs. This unifies the Savage-Squire-West construction with a recent algorithm for generating elimination trees of chordal graphs. Secondly, the second generalization is a Gray code for the quotients of lattices of acyclic orientations of chordal graphs, addressing a question raised by Pilaud (2022). This also generalizes a recent algorithm for generating lattice congruences of the weak order on the symmetric group. The algorithms are derived from the Hartung-Hoang-Mütze-Williams combinatorial generation framework, and they yield simple algorithms for computing Hamilton paths and cycles on large classes of polytopes, including chordal nestohedra and quotientopes.

Joint work with Jean Cardinal, Arturo Merino, Ondřej Mička, and Torsten Mütze.

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