65 research outputs found
An Axiomatic Approach to Routing
Information delivery in a network of agents is a key issue for large, complex
systems that need to do so in a predictable, efficient manner. The delivery of
information in such multi-agent systems is typically implemented through
routing protocols that determine how information flows through the network.
Different routing protocols exist each with its own benefits, but it is
generally unclear which properties can be successfully combined within a given
algorithm. We approach this problem from the axiomatic point of view, i.e., we
try to establish what are the properties we would seek to see in such a system,
and examine the different properties which uniquely define common routing
algorithms used today.
We examine several desirable properties, such as robustness, which ensures
adding nodes and edges does not change the routing in a radical, unpredictable
ways; and properties that depend on the operating environment, such as an
"economic model", where nodes choose their paths based on the cost they are
charged to pass information to the next node. We proceed to fully characterize
minimal spanning tree, shortest path, and weakest link routing algorithms,
showing a tight set of axioms for each.Comment: In Proceedings TARK 2015, arXiv:1606.0729
A Local-Dominance Theory of Voting Equilibria
It is well known that no reasonable voting rule is strategyproof. Moreover,
the common Plurality rule is particularly prone to strategic behavior of the
voters and empirical studies show that people often vote strategically in
practice. Multiple game-theoretic models have been proposed to better
understand and predict such behavior and the outcomes it induces. However,
these models often make unrealistic assumptions regarding voters' behavior and
the information on which they base their vote.
We suggest a new model for strategic voting that takes into account voters'
bounded rationality, as well as their limited access to reliable information.
We introduce a simple behavioral heuristic based on \emph{local dominance},
where each voter considers a set of possible world states without assigning
probabilities to them. This set is constructed based on prospective candidates'
scores (e.g., available from an inaccurate poll). In a \emph{voting
equilibrium}, all voters vote for candidates not dominated within the set of
possible states.
We prove that these voting equilibria exist in the Plurality rule for a broad
class of local dominance relations (that is, different ways to decide which
states are possible). Furthermore, we show that in an iterative setting where
voters may repeatedly change their vote, local dominance-based dynamics quickly
converge to an equilibrium if voters start from the truthful state. Weaker
convergence guarantees in more general settings are also provided.
Using extensive simulations of strategic voting on generated and real
preference profiles, we show that convergence is fast and robust, that emerging
equilibria are consistent across various starting conditions, and that they
replicate widely known patterns of human voting behavior such as Duverger's
law. Further, strategic voting generally improves the quality of the winner
compared to truthful voting
Heuristic Voting as Ordinal Dominance Strategies
Decision making under uncertainty is a key component of many AI settings, and
in particular of voting scenarios where strategic agents are trying to reach a
joint decision. The common approach to handle uncertainty is by maximizing
expected utility, which requires a cardinal utility function as well as
detailed probabilistic information. However, often such probabilities are not
easy to estimate or apply.
To this end, we present a framework that allows "shades of gray" of
likelihood without probabilities. Specifically, we create a hierarchy of sets
of world states based on a prospective poll, with inner sets contain more
likely outcomes. This hierarchy of likelihoods allows us to define what we term
ordinally-dominated strategies. We use this approach to justify various known
voting heuristics as bounded-rational strategies.Comment: This is the full version of paper #6080 accepted to AAAI'1
The Pricing War Continues: On Competitive Multi-Item Pricing
We study a game with \emph{strategic} vendors who own multiple items and a
single buyer with a submodular valuation function. The goal of the vendors is
to maximize their revenue via pricing of the items, given that the buyer will
buy the set of items that maximizes his net payoff.
We show this game may not always have a pure Nash equilibrium, in contrast to
previous results for the special case where each vendor owns a single item. We
do so by relating our game to an intermediate, discrete game in which the
vendors only choose the available items, and their prices are set exogenously
afterwards.
We further make use of the intermediate game to provide tight bounds on the
price of anarchy for the subset games that have pure Nash equilibria; we find
that the optimal PoA reached in the previous special cases does not hold, but
only a logarithmic one.
Finally, we show that for a special case of submodular functions, efficient
pure Nash equilibria always exist
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