Jean Derks

A shapley value for games with restricted coalitions

A “restriction” is a monotonic projection assigning to each coalition of a finite player setN a subcoalition. On the class of transferable utility games with player setN, a Shapley value is associated with each restriction by replacing, in the familiar probabilistic formula, each coalition by the subcoalition assigned to it. Alternatively, such a Shapley value can be characterized by restricted dividends. This method generalizes several other approaches known in literature. The main result is an axiomatic characterization with the property that the restriction is determined endogenously by the axioms.

The selectope for cooperative games

Abstract. The selectope of a cooperative transferable utility game is the convex hull of the payoff vectors obtained by assigning the Harsanyi dividends of the coalitions to members determined by so-called selectors. The selectope is studied from a set-theoretic point of view, as superset of the core and of the Weber set; and from a value-theoretic point of view, as containing weighted Shapley values, random order values, and sharing values.

Hierarchical organization structures and constraints on coalition formation

This paper studies the constraints in coalition formation that result from a hierarchical organization structure on the class of players in a cooperative game with transferable utilities. If one assumes that the superiors of a certain individual have to give permission to the actions undertaken by the individual, then one arrives at a limited collection of formable orautonomous coalitions. This resulting collection is a lattice of subsets on the player set.We show that if the collection of formable coalitions is limited to a lattice, the core allows for (infinite) exploitation of subordinates. For discerning lattices we are able to generalize the results of Weber (1988), namely the core is a subset of the convex hull of the collection of all attainable marginal contribution vectors plus a fixed cone. This relation is an equality if and only if the game is convex. This extends the results of Shapley (1971) and Ichiishi (1981).

Null Players Out? Linear Values For Games With Variable Supports

The paper studies the consequences of the Null Player Out (NPO) property for single-valued solutions on the class of cooperative games in characteristic function form. We allow for variable player populations (supports or carriers). A solution satisfies the NPO property, if elimination of a null player does not affect the payoffs of the other players. Our main emphasis lies on individual values. For linear values satisfying the null player property and a weak symmetry property, necessary and sufficient conditions for the NPO property are derived.

On the core of a collection of coalitions

Abstract. For a collection Ω of subsets of a finite set N we define its core to be equal to the polyhedral cone {x∈IRN: ∑i∈N xi=0 and ∑i∈Sxi≥0 for all S∈Ω}. This note describes several applications of this concept in the field of cooperative game theory. Especially collections Ω are considered with core equal to {0}. This property of a one-point core is proved to be equivalent to the non-degeneracy and balancedness of Ω. Further, the notion of exact cover is discussed and used in a second characterization of collections Ω with core equal to {0}.

Orderings, excess functions, and the nucleolus

The nucleolus of a cooperative game can be described with the aid of the leximin ordering but also on the basis of two other orderings. In this note the relation between these orderings is studied in a more general framework. The results are applied to the nucleolus corresponding to so-called normal excess functions. Also the Kohlberg criterion is extended to this more general case.

ON MERGE PROPERTIES OF THE SHAPLEY VALUE

Given a transferable utility game, where the players merge into subgroups described by a partition, we address the following question: under which conditions on the characteristic function and partition, merging is beneficial if the Shapley value is applied. Our results can be positioned among the search for well-defined classes of games where merging of players is possible without utility loss in case the Shapley value is chosen as the outcome of the game, and we will report on two of these classes of games arising from telecommunication problems.

Characterizations of the Random Order Values by Harsanyi Payoff Vectors

A Harsanyi payoff vector (see Vasil’ev in Optimizacija Vyp 21:30–35, 1978) of a cooperative game with transferable utilities is obtained by some distribution of the Harsanyi dividends of all coalitions among its members. Examples of Harsanyi payoff vectors are the marginal contribution vectors. The random order values (see Weber in The Shapley value, essays in honor of L.S. Shapley, Cambridge University Press, Cambridge, 1988) being the convex combinations of the marginal contribution vectors, are therefore elements of the Harsanyi set, which refers to the set of all Harsanyi payoff vectors.The aim of this paper is to provide two characterizations of the set of all sharing systems of the dividends whose associated Harsanyi payoff vectors are random order values. The first characterization yields the extreme points of this set of sharing systems and is based on a combinatorial result recently published (Vasil’ev in Discretnyi Analiz i Issledovaniye Operatsyi 10:17–55, 2003) the second characterization says that a Harsanyi payoff vector is a random order value iff the sharing system is strong monotonic.

Consistent restricted Shapley values

Transferable utility games with an additional power structure on the coalitions are considered. This power structure is not given explicitly, but only implicitly via a value; a value is a map that assigns an N-vector to every game with player set N. The implicit power structure is described by the concept of effectiveness of a coalition for a given value. The effectiveness of coalitions is constrained by axioms; in particular, the collection of effective coalitions is assumed to be closed under taking unions. Other axioms concern efficiency and consistency in a sense related to the consistency axiom of Hart and Mas-Colell. The main result of the paper is an axiomatic characterization of a class of restricted Shapley values, with the effective coalitions forming a lattice.

On cooperative games, inseparable by semivalues

Abstract.Semivalues like the Shapley value and the Banzhaf value may assign the same payoff vector to different games. It is even possible that two games attain the same outcome for all semivalues. Due to the linearity of the semivalues, this exactly occurs in case the difference of the two games is an element of the kernel of each semivalue. The intersection of these kernels is called the shared kernel, and its game theoretic importance is that two games can be evaluated differently by semivalues if and only if their difference is not a shared kernel element. The shared kernel is a linear subspace of games. The corresponding linear equality system is provided so that one is able to check membership. The shared kernel is spanned by specific {−1,0,1}-valued games, referred to as shuffle games. We provide a basis with shuffle games, based on an a-priori given ordering of the players.