5,082 research outputs found
Atomic Splittable Flow Over Time Games
In an atomic splittable flow over time game, finitely many players route flow dynamically through a network, in which edges are equipped with transit times, specifying the traversing time, and with capacities, restricting flow rates. Infinitesimally small flow particles controlled by the same player arrive at a constant rate at the player's origin and the player's goal is to maximize the flow volume that arrives at the player's destination within a given time horizon. Here, the flow dynamics are described by the deterministic queuing model, i.e., flow of different players merges perfectly, but excessive flow has to wait in a queue in front of the bottle-neck. In order to determine Nash equilibria in such games, the main challenge is to consider suitable definitions for the players' strategies, which depend on the level of information the players receive throughout the game. For the most restricted version, in which the players receive no information on the network state at all, we can show that there is no Nash equilibrium in general, not even for networks with only two edges. However, if the current edge congestions are provided over time, the players can adapt their route choices dynamically. We show that a profile of those strategies always lead to a unique feasible flow over time. Hence, those atomic splittable flow over time games are well-defined. For parallel-edge networks Nash equilibria exists and the total flow arriving in time equals the value of a maximum flow over time leading to a price of anarchy of 1.ISSN:1868-896
Load Balancing Congestion Games and their Asymptotic Behavior
A central question in routing games has been to establish conditions for the
uniqueness of the equilibrium, either in terms of network topology or in terms
of costs. This question is well understood in two classes of routing games. The
first is the non-atomic routing introduced by Wardrop on 1952 in the context of
road traffic in which each player (car) is infinitesimally small; a single car
has a negligible impact on the congestion. Each car wishes to minimize its
expected delay. Under arbitrary topology, such games are known to have a convex
potential and thus a unique equilibrium. The second framework is splitable
atomic games: there are finitely many players, each controlling the route of a
population of individuals (let them be cars in road traffic or packets in the
communication networks). In this paper, we study two other frameworks of
routing games in which each of several players has an integer number of
connections (which are population of packets) to route and where there is a
constraint that a connection cannot be split. Through a particular game with a
simple three link topology, we identify various novel and surprising properties
of games within these frameworks. We show in particular that equilibria are non
unique even in the potential game setting of Rosenthal with strictly convex
link costs. We further show that non-symmetric equilibria arise in symmetric
networks. I. INTRODUCTION A central question in routing games has been to
establish conditions for the uniqueness of the equilibria, either in terms of
the network topology or in terms of the costs. A survey on these issues is
given in [1]. The question of uniqueness of equilibria has been studied in two
different frameworks. The first, which we call F1, is the non-atomic routing
introduced by Wardrop on 1952 in the context of road traffic in which each
player (car) is infinitesimally small; a single car has a negligible impact on
the congestion. Each car wishes to minimize its expected delay. Under arbitrary
topology, such games are known to have a convex potential and thus have a
unique equilibrium [2]. The second framework, denoted by F2, is splitable
atomic games. There are finitely many players, each controlling the route of a
population of individuals. This type of games have already been studied in the
context of road traffic by Haurie and Marcotte [3] but have become central in
the telecom community to model routing decisions of Internet Service Providers
that can decide how to split the traffic of their subscribers among various
routes so as to minimize network congestion [4]. In this paper we study
properties of equilibria in two other frameworks of routing games which exhibit
surprisin
Unilateral Altruism in Network Routing Games with Atomic Players
We study a routing game in which one of the players unilaterally acts
altruistically by taking into consideration the latency cost of other players
as well as his own. By not playing selfishly, a player can not only improve the
other players' equilibrium utility but also improve his own equilibrium
utility. To quantify the effect, we define a metric called the Value of
Unilateral Altruism (VoU) to be the ratio of the equilibrium utility of the
altruistic user to the equilibrium utility he would have received in Nash
equilibrium if he were selfish. We show by example that the VoU, in a game with
nonlinear latency functions and atomic players, can be arbitrarily large. Since
the Nash equilibrium social welfare of this example is arbitrarily far from
social optimum, this example also has a Price of Anarchy (PoA) that is
unbounded. The example is driven by there being a small number of players since
the same example with non-atomic players yields a Nash equilibrium that is
fully efficient
Equilibrium Computation in Resource Allocation Games
We study the equilibrium computation problem for two classical resource
allocation games: atomic splittable congestion games and multimarket Cournot
oligopolies. For atomic splittable congestion games with singleton strategies
and player-specific affine cost functions, we devise the first polynomial time
algorithm computing a pure Nash equilibrium. Our algorithm is combinatorial and
computes the exact equilibrium assuming rational input. The idea is to compute
an equilibrium for an associated integrally-splittable singleton congestion
game in which the players can only split their demands in integral multiples of
a common packet size. While integral games have been considered in the
literature before, no polynomial time algorithm computing an equilibrium was
known. Also for this class, we devise the first polynomial time algorithm and
use it as a building block for our main algorithm.
We then develop a polynomial time computable transformation mapping a
multimarket Cournot competition game with firm-specific affine price functions
and quadratic costs to an associated atomic splittable congestion game as
described above. The transformation preserves equilibria in either games and,
thus, leads -- via our first algorithm -- to a polynomial time algorithm
computing Cournot equilibria. Finally, our analysis for integrally-splittable
games implies new bounds on the difference between real and integral Cournot
equilibria. The bounds can be seen as a generalization of the recent bounds for
single market oligopolies obtained by Todd [2016].Comment: This version contains some typo corrections onl
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