Lam, ThomasWilliams, Lauren2009-04-182008Lam, Thomas, and Lauren Williams. 2008. Total positivity for cominuscule Grassmannians. New York Journal of Mathematics 14.1076-9803http://nrs.harvard.edu/urn-3:HUL.InstRepos:2796935In this paper we explore the combinatorics of the non-negative part (G/P)+ of a cominuscule Grassmannian. For each such Grassmannian we define Le-diagrams -- certain fillings of generalized Young diagrams which are in bijection with the cells of (G/P)+. In the classical cases, we describe Le-diagrams explicitly in terms of pattern avoidance. We also define a game on diagrams, by which one can reduce an arbitrary diagram to a Le-diagram. We give enumerative results and relate our Le-diagrams to other combinatorial objects. Surprisingly, the totally non-negative cells in the open Schubert cell of the odd and even orthogonal Grassmannians are (essentially) in bijection with preference functions and atomic preference functions respectively.en-US