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E-HBA: Using Action Policies for Expert Advice and Agent Typification

AAAI Conferences

Past research has studied two approaches to utilise pre-defined policy sets in repeated interactions: as experts, to dictate our own actions, and as types, to characterise the behaviour of other agents. In this work, we bring these complementary views together in the form of a novel meta-algorithm, called Expert-HBA (E-HBA), which can be applied to any expert algorithm that considers the average (or total) payoff an expert has yielded in the past. E-HBA gradually mixes the past payoff with a predicted future payoff, which is computed using the type-based characterisation. We present results from a comprehensive set of repeated matrix games, comparing the performance of several well-known expert algorithms with and without the aid of E-HBA. Our results show that E-HBA has the potential to significantly improve the performance of expert algorithms.


Endgame Solving in Large Imperfect-Information Games

AAAI Conferences

The leading approach for computing strong game-theoretic strategies in large imperfect-information games is to first solve an abstracted version of the game offline, then perform a table lookup during game play. We consider a modification to this approach where we solve the portion of the game that we have actually reached in real time to a greater degree of accuracy than in the initial computation. We call this approach endgame solving. Theoretically, we show that endgame solving can produce highly exploitable strategies in some games; however, we show that it can guarantee a low exploitability in certain games where the opponent is given sufficient exploitative power within the endgame. Furthermore, despite the lack of a general worst-case guarantee, we describe many benefits of endgame solving. We present an efficient algorithm for performing endgame solving in large imperfect-information games, and present a new variance-reduction technique for evaluating the performance of an agent that uses endgame solving. Experiments on no-limit Texas Hold'em show that our algorithm leads to significantly stronger performance against the strongest agents from the 2013 AAAI Annual Computer Poker Competition.


Modeling Spatial-Temporal Dynamics of Human Movements for Predicting Future Trajectories

AAAI Conferences

This paper presents a novel approach to modeling the dynamics of human movements with a grid-based representation.For each grid cell, we formulate the local dynamics using a variant of the left-to-right HMM, and thus explicitly model the exiting direction from the current cell. The dependency of this process on the entry direction is captured by employing the Input-Output HMM (IOHMM). On a higher level, we introduce the place where the whole trajectory originated into the IOHMM framework forming a hierarchical input structure. Therefore, we manage to capture both local spatial-temporal correlations and the long-term dependency on faraway initiating events, thus enabling the developed model to incorporate more information and to generate more informative predictions of future trajectories.The experimental results in an office corridor environment verify the capabilities of our method.


Real-Time Optimal Selection of Multirobot Coalition Formation Algorithms Using Conceptual Clustering

AAAI Conferences

The presented framework is the The multirobot coalition formation problem seeks to intelligently first to leverage a conceptual clustering technique to partition partition a team of heterogeneous robots into any set of coalition formation algorithms in order to derive coalitions for a set of real-world tasks. Besides being N Pan optimal hierarchy classification tree, given any classification complete (Sandholm et al. 1999), the problem is also hard taxonomy. The results contribute to the state-ofthe-art to approximate (Service and Adams 2011a). Traditional approaches in multiagent systems by demonstrating the existence to solving the problem include a number of greedy of crucial patterns and intricate relationships among existing algorithms (Shehory and Kraus 1998; Vig and Adams coalition algorithms.


What Predicts Media Coverage of Health Science Articles?

AAAI Conferences

An important aspect of health science is communicating research findings to the public. The media is a critical instrument in disseminating research. Yet the process by which a scientific article becomes “newsworthy” is not well understood. In this study, we use large-scale text analysis to characterize the content features of articles that are predictive of newsworthiness. We experiment with two novel corpora: (i) 28,910 articles from a di- verse range of biomedical and health journals, of which 1,343 were covered by the news agency Reuters, and (ii) 10,760 articles from the JAMA journals, of which 846 were given press releases by the journal editors. We show that media coverage can be predicted reasonably well: logistic regression achieves mean AUCs of 0.783 and 0.882 on the Reuters and JAMA datasets, respec- tively. We present and discuss interesting findings con- cerning the most predictive content features.


The Impact of Determinism on Learning Atari 2600 Games

AAAI Conferences

Atari 2600 games are deterministic given a fixed policy leading to a fixed sequence of actions. This article investigates three methods for adding randomness: random initialization, epsilon-greedy action selection, and epislon-repeat action selection. These methods are evaluated by how well they are able to derail a memorizing agent without hurting the performance of a randomized agent. Results indicate that epsilon-repeat action selection best fits the desired criteria and lower values of epsilon than previously used are sufficient to derail the memorizing agent.


Two Algorithms for the Movements of Robotic Bodyguard Teams

AAAI Conferences

In this paper we consider a scenario where one or more robotic bodyguards are protecting an important individual (VIP) moving in a public space against harassment or harm from unarmed civilians. In this scenario, the main objective of the robots is to position themselves such that at any given moment they provide maximum physical cover for the VIP. The robots need to follow the VIP in its movement and take into account the movements of the civilians as well. The environment can also contain obstacles which present challenges to movement but also provide natural cover. We designed two algorithms for the movement of the bodyguard robots: Threat Vector Resolution (TVR) for a single robot and Quadrant Load Balancing (QLB) for teams of bodyguard robots. We evaluated the proposed approaches against rigid formations in a simulation study.


A Solution Alternative to Achieve Parcel Connectivity in the Dynamic Reserve Design Problem

AAAI Conferences

The DNR is able to purchase lands and engage in conservation easements, but there is considerable uncertainty (for the Conservation reserve design is the problem of selecting reasons enumerated above) about which lands to target, and parcels of land such that the assembled set maximizes when. Furthermore, for any parcel that is protected through some criterion pertaining to the conservation of species or purchase or easement, DNR encumbers a responsibility to natural communities (Williams, ReVelle, and Levin 2005).


Predicting Bike Usage for New York City’s Bike Sharing System

AAAI Conferences

Bike sharing systems consist of a fleet of bikes placed in a network of docking stations. These bikes can then be rented and returned to any of the docking stations after usage. Predicting unrealized bike demand at locations currently without bike stations is important for effectively designing and expanding bike sharing systems. We predict pairwise bike demand for New York City’s Citi Bike system. Since the system is driven by daily commuters we focus only on the morning rush hours between 7:00 AM to 11:00 AM during weekdays. We use taxi usage, weather and spatial variables as covariates to predict bike demand, and further analyze the influence of precipitation and day of week. We show that aggregating stations in neighborhoods can substantially improve predictions. The presented model can assist planners by predicting bike demand at a macroscopic level, between pairs of neighborhoods.


Encoding Time Series as Images for Visual Inspection and Classification Using Tiled Convolutional Neural Networks

AAAI Conferences

Inspired by recent successes of deep learning in computer vision and speech recognition, we propose a novel framework to encode time series data as different types of images, namely, Gramian Angular Fields (GAF) and Markov Transition Fields (MTF). This enables the use of techniques from computer vision for classification. Using a polar coordinate system, GAF images are represented as a Gramian matrix where each element is the trigonometric sum (i.e., superposition of directions) between different time intervals. MTF images represent the first order Markov transition probability along one dimension and temporal dependency along the other. We used Tiled Convolutional Neural Networks (tiled CNNs) on 12 standard datasets to learn high-level features from individual GAF, MTF, and GAF-MTF images that resulted from combining GAF and MTF representations into a single image. The classification results of our approach are competitive with five stateof-the-art approaches. An analysis of the features and weights learned via tiled CNNs explains why the approach works.