4,779 research outputs found
Understanding contextualised rational action - author's response
Understanding contextualised rational action - author's respons
The Network Improvement Problem for Equilibrium Routing
In routing games, agents pick their routes through a network to minimize
their own delay. A primary concern for the network designer in routing games is
the average agent delay at equilibrium. A number of methods to control this
average delay have received substantial attention, including network tolls,
Stackelberg routing, and edge removal.
A related approach with arguably greater practical relevance is that of
making investments in improvements to the edges of the network, so that, for a
given investment budget, the average delay at equilibrium in the improved
network is minimized. This problem has received considerable attention in the
literature on transportation research and a number of different algorithms have
been studied. To our knowledge, none of this work gives guarantees on the
output quality of any polynomial-time algorithm. We study a model for this
problem introduced in transportation research literature, and present both
hardness results and algorithms that obtain nearly optimal performance
guarantees.
- We first show that a simple algorithm obtains good approximation guarantees
for the problem. Despite its simplicity, we show that for affine delays the
approximation ratio of 4/3 obtained by the algorithm cannot be improved.
- To obtain better results, we then consider restricted topologies. For
graphs consisting of parallel paths with affine delay functions we give an
optimal algorithm. However, for graphs that consist of a series of parallel
links, we show the problem is weakly NP-hard.
- Finally, we consider the problem in series-parallel graphs, and give an
FPTAS for this case.
Our work thus formalizes the intuition held by transportation researchers
that the network improvement problem is hard, and presents topology-dependent
algorithms that have provably tight approximation guarantees.Comment: 27 pages (including abstract), 3 figure
Market regulation and firm performance: the case of smoking bans in the UK
This paper analyzes the effects of a ban on smoking in public places upon firms and
consumers. It presents a theoretical model and tests its predictions using unique data from
before and after the introduction of smoking bans in the UK. Cigarette smoke is a public bad,
and smokers and non-smokers differ in their valuation of smoke-free amenities. Consumer
heterogeneity implies that the market equilibrium may result in too much uniformity, whereas
social optimality requires a mix of smoking and non-smoking pubs (which can be
operationalized via licensing). If the market equilibrium has almost all pubs permitting
smoking (as is the case in the data) then a blanket ban reduces pub sales, profits, and
consumer welfare. We collect survey data from public houses and find that the Scottish
smoking ban (introduced in March 2006) reduced pub sales and harmed medium run
profitability. An event study analysis of the stock market performance of pub-holding
companies corroborates the negative effects of the smoking ban on firm performance
A Foundation for Markov Equilibria in Infinite Horizon Perfect Information Games
We study perfect information games with an infinite horizon played by an arbitrary number of players. This class of games includes infinitely repeated perfect information games, repeated games with asynchronous moves, games with long and short run players, games with overlapping generations of players, and canonical non-cooperative models of bargaining. We consider two restrictions on equilibria. An equilibrium is purifiable if close by behavior is consistent with equilibrium when agentsâ payoffs at each node are perturbed additively and independently. An equilibrium has bounded recall if there exists K such that at most one playerâs strategy depends on what happened more than K periods earlier. We show that only Markov equilibria have bounded memory and are purifiable. Thus if a game has at most one long-run player, all purifiable equilibria are Markov.Markov, bounded recall, purification
Purification in the Infinitely-Repeated Prisonersâ Dilemma, Second Version
This paper investigates the Harsanyi (1973)-purifiability of mixed strategies in the repeated prisonersâ dilemma with perfect monitoring. We perturb the game so that in each period, a player receives a private payoff shock which is independently and identically distributed across players and periods. We focus on the purifiability of one-period memory mixed strategy equilibria used by Ely and Välimäki (2002) in their study of the repeated prisonersâ dilemma with private monitoring. We find that any such strategy profile is not the limit of one-period memory equilibrium strategy profiles of the perturbed game, for almost all noise distributions. However, if we allow infinite memory strategies in the perturbed game, then any completely-mixed equilibrium is purifiable.Purification, belief-free equilibria, repeated games
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