Parking functions: interdisciplinary connections

Suppose that m drivers each choose a preferred parking space in a linear car park with n spots. In order, each driver goes to their chosen spot and parks there if possible, and otherwise takes the next available spot if it exists. If all drivers park successfully, the sequence of choices is called a parking function. Classical parking functions correspond to the case .

We investigate various probabilistic properties of a uniform parking function. Through a combinatorial construction termed a parking function multi-shuffle, we give a formula for the law of multiple coordinates in the generic situation . We further deduce all possible covariances: between two coordinates, between a coordinate and an unattempted spot, and between two unattempted spots. This asymptotic scenario in the generic situation is in sharp contrast with that of the special situation .

A generalization of parking functions called interval parking functions is also studied, in which each driver is willing to park only in a fixed interval of spots. We construct a family of bijections between interval parking functions with n cars and n spots and edge-labeled spanning trees with vertices and a specified root.

On the square root of the inverse different

Let be a finite Galois-algebra extension of a number field F, with group G. Suppose that is weakly ramified and that the square root of the inverse different is defined. (This latter condition holds if, for example, is odd.) Erez has conjectured that the class of in the locally free class group of is equal to the Cassou–Noguès–Fröhlich root number class associated with . This conjecture has been verified in many cases. We establish a precise formula for in terms of in all cases where is defined and is tame, and are thereby able to deduce that, in general, is not equal to .