Expectations of Tutte-related functions of random ranked sets with multiplicities

Employing two models, we show that various counting functions of a random variable defined by restriction or contraction of a ranked set with multiplicity (e.g., classical and arithmetic matroids) have expectations given by the corresponding multivariate Tutte polynomial. The first model is based on a generalization of a convolution formula of Kung (2010), extending from matroids to ranked sets with multiplicities. This model enables us to compute the expectations of many familiar polynomials, such as the chromatic, flow and Ehrhart polynomials, generalizing the classical results of Welsh (1996) on random graphs. The second model is designed to compute the expectations of invariants that are generally not evaluations of the polynomials mentioned above, such as the number of connected components of an intersection of hypersurfaces in an abelian Lie group arrangement, and the number of lattice points in a half-open zonotope. In particular, both models yield new probabilistic interpretations of the arithmetic Tutte polynomial and $G$-Tutte polynomial. A simple convolution-like formula for the Ehrhart polynomials of lattice zonotopes which seems to be new will also be given.