The order of birational rowmotion

Darij Grinberg (1) , Tom Roby (2)

1 MIT - Massachusetts Institute of Technology
2 UCONN - University of Connecticut

Various authors have studied a natural operation (under various names) on the order ideals (equivalently antichains) of a finite poset, here called \emphrowmotion. For certain posets of interest, the order of this map is much smaller than one would naively expect, and the orbits exhibit unexpected properties. In very recent work (inspired by discussions with Berenstein) Einstein and Propp describe how rowmotion can be generalized: first to the piecewise-linear setting of order polytopes, then via detropicalization to the birational setting. In the latter setting, it is no longer \empha priori clear even that birational rowmotion has finite order, and for many posets the order is infinite. However, we are able to show that birational rowmotion has the same order, p+q, for the poset P=[p]×[q] (product of two chains), as ordinary rowmotion. We also show that birational (hence ordinary) rowmotion has finite order for some other classes of posets, e.g., the upper, lower, right and left halves of the poset above, and trees having all leaves on the same level. Our methods are based on those used by Volkov to resolve the type AA (rectangular) Zamolodchikov Periodicity Conjecture.

Mots clés: antichains; birational actions; birational rowmotion; Brouwer-Schrijver map; cluster algebras; orbit; order ideals; Panyushev complementation; poset; product of chains; promotion; rowmotion; toggle group; Zamolodchikov conjecture.

Domaines: Mathématique discrète [cs.DM]; Combinatoire [math.CO]

Darij Grinberg, Tom Roby. The order of birational rowmotion. 26th International Conference on Formal Power Series and Algebraic Combinatorics (FPSAC 2014), 2014, Chicago, United States. pp.753-764, ⟨10.46298/dmtcs.2439⟩. ⟨hal-01207567⟩