How to Play 3x3-Games A Strategy Method Experiment

We report an experiment that uses the strategy method (Selten 1967) to elicit subjects' general strategy for playing any 2-person 3x3-game with integer payoffs between 0 and 99. Each two subjects' strategies play 500000 games in each of the 5 tournaments. For games with pure strategy equilibria (ca. 80%), the frequency of pure strategy equilibrium play increases from 51% in the first to 74% in the last tournament, in which there is equilibrium play in 98% of all games with only one pure equilibrium. In games with more than one pure equilibrium, a tendency towards the selection of the one with the maximum joint payoff is observed. For games without pure equilibria, subjects’ strategies do not search for mixed equilibria. The strategy programs are based on much simpler strategic concepts combined in various ways. The simplest one is MAP, maximal average payoff, the strategy which maximizes the sum of the three payoffs obtainable against the possible choices of the other player. BR-MAP, the best reply to MAP, and BR-BR-MAP, the best reply to BR-MAP, are also important ingredients of the strategy programs. Together these three form a hierarchy to which we refer to as the best-reply cascade.2-person games, experimental economics

A Model of B2B Exchanges

B2B exchanges are revolutionizing the way businesses will buy and sell a variety of intermediary products and services. It is estimated that most of the roughly $7 trillion worth of business transactions are likely to go through these new institutions within the next decade. This paper tries to understand the economics governing the transactions within B2B exchanges and analyze their likely evolution over time. In doing so, we start by providing the rigorous definitions to a number of critical concepts broadly used in the context of B2B exchanges including "market fragmentation", "critical mass" and buyer-seller "connectivity". We describe equilibrium behavior in the exchange and analyze it as a function of these critical concepts. Next, we study the evolution of the exchanges in a dynamic system where buyers and sellers enter (exit) the exchange based on the relative economic surplus (loss) they receive inside vs. outside the exchange. Our results have important implications for practice. For example, we show that equilibrium prices within the marketplace may not always decrease with lower search costs. However, buyer surplus rises with lower search costs even if prices are higher in the exchange. We also show that the general view that demand and supply (so-called "liquidity") either grows or shrinks in the marketplace may not always hold and it is quite possible to have a marketplace that is stable even though only a relatively small proportion of the market participants transact in it. Finally, we also provide conditions under which the exchange should subsidize buyers or seller in order to achieve critical mass.

Almost-dominant Strategy Implementation

Though some economic environments provide allocation rules that are implementable in dominant strategies (strategy-proof), a significant number of environments yield impossibility results. On the other hand, while there are quite general possibility results regarding implementation in Nash or Bayesian equilibrium, these equilibrium concepts make strong assumptions about the knowledge that players possess, or about the way they deal with uncertainty. As a compromise between these two notions, we propose a solution concept built on one premise: Players who do not have much to gain by manipulating an allocation rule will not bother to manipulate it. We search for efficient allocation rules for 2-agent exchange economies that never provide players with large gains from cheating. Though we show that such rules are very inequitable, we also show that some such rules are significantly more flexible than those that satisfy the stronger condition of strategy-proofness.Strategy-proof, almost dominant strategy

Neuroevolutionary learning of particles and protocols for self-assembly

Within simulations of molecules deposited on a surface we show that neuroevolutionary learning can design particles and time-dependent protocols to promote self-assembly, without input from physical concepts such as thermal equilibrium or mechanical stability and without prior knowledge of candidate or competing structures. The learning algorithm is capable of both directed and exploratory design: it can assemble a material with a user-defined property, or search for novelty in the space of specified order parameters. In the latter mode it explores the space of what can be made rather than the space of structures that are low in energy but not necessarily kinetically accessible

How to shift bias: Lessons from the Baldwin effect

An inductive learning algorithm takes a set of data as input and generates a hypothesis as output. A set of data is typically consistent with an infinite number of hypotheses; therefore, there must be factors other than the data that determine the output of the learning algorithm. In machine learning, these other factors are called the bias of the learner. Classical learning algorithms have a fixed bias, implicit in their design. Recently developed learning algorithms dynamically adjust their bias as they search for a hypothesis. Algorithms that shift bias in this manner are not as well understood as classical algorithms. In this paper, we show that the Baldwin effect has implications for the design and analysis of bias shifting algorithms. The Baldwin effect was proposed in 1896, to explain how phenomena that might appear to require Lamarckian evolution (inheritance of acquired characteristics) can arise from purely Darwinian evolution. Hinton and Nowlan presented a computational model of the Baldwin effect in 1987. We explore a variation on their model, which we constructed explicitly to illustrate the lessons that the Baldwin effect has for research in bias shifting algorithms. The main lesson is that it appears that a good strategy for shift of bias in a learning algorithm is to begin with a weak bias and gradually shift to a strong bias