Search Results for author: Christos Dimitrakakis

Found 35 papers, 4 papers with code

Eliciting Kemeny Rankings

1 code implementation18 Dec 2023 Anne-Marie George, Christos Dimitrakakis

Furthermore, if all agents' preferences are strict rankings over the alternatives, we provide means to prune confidence intervals and thereby guide a more efficient elicitation.

Bandits Meet Mechanism Design to Combat Clickbait in Online Recommendation

no code implementations27 Nov 2023 Thomas Kleine Buening, Aadirupa Saha, Christos Dimitrakakis, Haifeng Xu

We study a strategic variant of the multi-armed bandit problem, which we coin the strategic click-bandit.

Minimax-Bayes Reinforcement Learning

1 code implementation21 Feb 2023 Thomas Kleine Buening, Christos Dimitrakakis, Hannes Eriksson, Divya Grover, Emilio Jorge

While the Bayesian decision-theoretic framework offers an elegant solution to the problem of decision making under uncertainty, one question is how to appropriately select the prior distribution.

Decision Making Decision Making Under Uncertainty +2

Environment Design for Inverse Reinforcement Learning

no code implementations26 Oct 2022 Thomas Kleine Buening, Christos Dimitrakakis

The task of learning a reward function from expert demonstrations suffers from high sample complexity as well as inherent limitations to what can be learned from demonstrations in a given environment.

reinforcement-learning Reinforcement Learning (RL)

Risk-Sensitive Bayesian Games for Multi-Agent Reinforcement Learning under Policy Uncertainty

no code implementations18 Mar 2022 Hannes Eriksson, Debabrota Basu, Mina Alibeigi, Christos Dimitrakakis

In existing literature, the risk in stochastic games has been studied in terms of the inherent uncertainty evoked by the variability of transitions and actions.

Multi-agent Reinforcement Learning reinforcement-learning +1

Interactive Inverse Reinforcement Learning for Cooperative Games

no code implementations8 Nov 2021 Thomas Kleine Buening, Anne-Marie George, Christos Dimitrakakis

How should the first agent act in order to learn the joint reward function as quickly as possible and so that the joint policy is as close to optimal as possible?

reinforcement-learning Reinforcement Learning (RL)

High-dimensional near-optimal experiment design for drug discovery via Bayesian sparse sampling

no code implementations23 Apr 2021 Hannes Eriksson, Christos Dimitrakakis, Lars Carlsson

We study the problem of performing automated experiment design for drug screening through Bayesian inference and optimisation.

Bayesian Inference Drug Discovery +2

Adaptive Belief Discretization for POMDP Planning

1 code implementation15 Apr 2021 Divya Grover, Christos Dimitrakakis

We instead propose an adaptive belief discretization scheme, and give its associated planning error.

Near-optimal Bayesian Solution For Unknown Discrete Markov Decision Process

no code implementations20 Jun 2019 Aristide Tossou, Christos Dimitrakakis, Debabrota Basu

We derive the first polynomial time Bayesian algorithm, BUCRL{} that achieves up to logarithm factors, a regret (i. e the difference between the accumulated rewards of the optimal policy and our algorithm) of the optimal order $\tilde{\mathcal{O}}(\sqrt{DSAT})$.

Epistemic Risk-Sensitive Reinforcement Learning

no code implementations14 Jun 2019 Hannes Eriksson, Christos Dimitrakakis

The risk-averse behavior is then compared with the behavior of the optimal risk-neutral policy in environments with epistemic risk.

reinforcement-learning Reinforcement Learning (RL)

Near-Optimal Online Egalitarian learning in General Sum Repeated Matrix Games

no code implementations4 Jun 2019 Aristide Tossou, Christos Dimitrakakis, Jaroslaw Rzepecki, Katja Hofmann

We study two-player general sum repeated finite games where the rewards of each player are generated from an unknown distribution.

Differential Privacy for Multi-armed Bandits: What Is It and What Is Its Cost?

no code implementations29 May 2019 Debabrota Basu, Christos Dimitrakakis, Aristide Tossou

We derive and contrast lower bounds on the regret of bandit algorithms satisfying these definitions.

Multi-Armed Bandits

Randomised Bayesian Least-Squares Policy Iteration

no code implementations6 Apr 2019 Nikolaos Tziortziotis, Christos Dimitrakakis, Michalis Vazirgiannis

We introduce Bayesian least-squares policy iteration (BLSPI), an off-policy, model-free, policy iteration algorithm that uses the Bayesian least-squares temporal-difference (BLSTD) learning algorithm to evaluate policies.

Thompson Sampling

On The Differential Privacy of Thompson Sampling With Gaussian Prior

no code implementations24 Jun 2018 Aristide C. Y. Tossou, Christos Dimitrakakis

This compares favorably to the previous result for Thompson Sampling in the literature ((Mishra & Thakurta, 2015)) which adds a term of $\mathcal{O}(\frac{K \ln^3 T}{\epsilon^2})$ to the regret in order to achieve the same privacy level.

Thompson Sampling

Multi-View Decision Processes: The Helper-AI Problem

no code implementations NeurIPS 2017 Christos Dimitrakakis, David C. Parkes, Goran Radanovic, Paul Tylkin

We consider a two-player sequential game in which agents have the same reward function but may disagree on the transition probabilities of an underlying Markovian model of the world.

Learning to Match

no code implementations30 Jul 2017 Philip Ekman, Sebastian Bellevik, Christos Dimitrakakis, Aristide Tossou

One specific such problem involves matching a set of workers to a set of tasks.

Calibrated Fairness in Bandits

no code implementations6 Jul 2017 Yang Liu, Goran Radanovic, Christos Dimitrakakis, Debmalya Mandal, David C. Parkes

In addition, we define the {\em fairness regret}, which corresponds to the degree to which an algorithm is not calibrated, where perfect calibration requires that the probability of selecting an arm is equal to the probability with which the arm has the best quality realization.

Decision Making Fairness +1

Bayesian fairness

no code implementations31 May 2017 Christos Dimitrakakis, Yang Liu, David Parkes, Goran Radanovic

We consider the problem of how decision making can be fair when the underlying probabilistic model of the world is not known with certainty.

BIG-bench Machine Learning Decision Making +1

Achieving Privacy in the Adversarial Multi-Armed Bandit

no code implementations16 Jan 2017 Aristide C. Y. Tossou, Christos Dimitrakakis

This allows us to reach $\mathcal{O}{(\sqrt{\ln T})}$-DP, with a regret of $\mathcal{O}{(T^{2/3})}$ that holds against an adaptive adversary, an improvement from the best known of $\mathcal{O}{(T^{3/4})}$.

Thompson Sampling For Stochastic Bandits with Graph Feedback

no code implementations16 Jan 2017 Aristide C. Y. Tossou, Christos Dimitrakakis, Devdatt Dubhashi

We present a novel extension of Thompson Sampling for stochastic sequential decision problems with graph feedback, even when the graph structure itself is unknown and/or changing.

Thompson Sampling

On the Differential Privacy of Bayesian Inference

no code implementations22 Dec 2015 Zuhe Zhang, Benjamin Rubinstein, Christos Dimitrakakis

We study how to communicate findings of Bayesian inference to third parties, while preserving the strong guarantee of differential privacy.

Bayesian Inference

Algorithms for Differentially Private Multi-Armed Bandits

no code implementations27 Nov 2015 Aristide Tossou, Christos Dimitrakakis

This is a significant improvement over previous results, which only achieve poly-log regret $O(\epsilon^{-2} \log^{2} T)$, because of our use of a novel interval-based mechanism.

Multi-Armed Bandits

Generalised Entropy MDPs and Minimax Regret

no code implementations10 Dec 2014 Emmanouil G. Androulakis, Christos Dimitrakakis

Bayesian methods suffer from the problem of how to specify prior beliefs.

Probabilistic inverse reinforcement learning in unknown environments

no code implementations9 Aug 2014 Aristide Tossou, Christos Dimitrakakis

To do so, we extend previous probabilistic approaches for inverse reinforcement learning in known MDPs to the case of unknown dynamics or opponents.

Bayesian Inference reinforcement-learning +1

Probabilistic inverse reinforcement learning in unknown environments

no code implementations14 Jul 2013 Aristide C. Y. Tossou, Christos Dimitrakakis

To do so, we extend previous probabilistic approaches for inverse reinforcement learning in known MDPs to the case of unknown dynamics or opponents.

Bayesian Inference reinforcement-learning +1

Bayesian Differential Privacy through Posterior Sampling

no code implementations5 Jun 2013 Christos Dimitrakakis, Blaine Nelson, and Zuhe Zhang, Aikaterini Mitrokotsa, Benjamin Rubinstein

All our general results hold for arbitrary database metrics, including those for the common definition of differential privacy.

Bayesian Inference Privacy Preserving

ABC Reinforcement Learning

no code implementations27 Mar 2013 Christos Dimitrakakis, Nikolaos Tziortziotis

This paper introduces a simple, general framework for likelihood-free Bayesian reinforcement learning, through Approximate Bayesian Computation (ABC).

reinforcement-learning Reinforcement Learning (RL)

Personalized News Recommendation with Context Trees

no code implementations4 Mar 2013 Florent Garcin, Christos Dimitrakakis, Boi Faltings

The profusion of online news articles makes it difficult to find interesting articles, a problem that can be assuaged by using a recommender system to bring the most relevant news stories to readers.

News Recommendation Recommendation Systems

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