Journal of Combinatorics

Volume 9 (2018)

Number 2

Combinatorics of symmetric plabic graphs

Pages: 259 – 278

DOI: http://dx.doi.org/10.4310/JOC.2018.v9.n2.a3

Authors

Rachel Karpman (Department of Mathematics, University of Michigan, Ann Arbor, Mich., U.S.A.)

Yi Su (Department of Mathematics, University of Michigan, Ann Arbor, Mich., U.S.A.)

Abstract

A plabic graph is a planar bicolored graph embedded in a disk, which satisfies some combinatorial conditions. Postnikov’s boundary measurement map takes the space of positive edge weights of a plabic graph G to a positroid cell in a totally nonnegative Grassmannian. In this note, we investigate plabic graphs which are symmetric about a line of reflection, up to reversing the colors of vertices. These symmetric plabic graphs arise naturally in the study of total positivity for the Lagrangian Grassmannian. We characterize various combinatorial objects associated with symmetric plabic graphs, and describe the subset of a Grassmannian which can be realized by symmetric weightings of symmetric plabic graphs.

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Rachel Karpman is supported in part by NSF grant DGE-1256260 and NSF grant DMS-0943832.

Received 18 October 2016

Published 22 January 2018