arXiv subjects

Ath. Kehagias

Publications and source records attributed to Ath. Kehagias.

10 recordsLinked to original sources

arXiv2024

Static Nuel Games with Terminal Payoff

In this paper we study a variant of the Nuel game (a generalization of the duel) which is played in turns by $N$ players. In each turn a single player must fire at one of the other players and has a certain probability of hitting and killing his target. The players shoot in a fixed sequence and when a player is eliminated, the ``move'' passes to the next surviving player. The winner is the last surviving player. We prove that, for every $N\geq2$, the Nuel has a stationary Nash equilibrium and provide algorithms for its computation.

cs.DM↗

arXiv2024

A Game Theoretic Analysis of the Three-Gambler Ruin Game

We study the following game. Three players start with initial capitals of $s_{1},s_{2},s_{3}$ dollars; in each round player $P_{m}$ is selected with probability $\frac{1}{3}$; then \emph{he} selects player $P_{n}$ and they play a game in which $P_{m}$ wins from (resp. loses to) $P_{n}$ one dollar with probability $p_{mn}$ (resp. $p_{nm}=1-p_{mn}$). When a player loses all his capital he drops out; the game continues until a single player wins by collecting everybody's money. This is a "strategic" version of the classical Gambler's Ruin game. It seems reasonable that a player may improve his winning probability by judicious selection of which opponent to engage in each round. We formulate the situation as a \emph{stochastic game} and prove that it has at least one Nash equilibrium in deterministic stationary strategies.

cs.GT↗

arXiv2021

An Algorithm for Limited Visibility Graph Searching

We study a graph search problem in which a team of searchers attempts to find a mobile target located in a graph. Assuming that (a) the visibility field of the searchers is limited, (b) the searchers have unit speed and (c) the target has infinite speed, we formulate the Limited Visibility Graph Search (LVGS) problem and present the LVGS algorithm, which produces a search schedule guaranteed to find the target in the minimum possible number of steps. Our LVGS algorithm is a conversion of Guibas and Lavalle's polygonal region search algorithm.

cs.DM↗

arXiv2018

Selfish Cops and Active Robber: Multi-Player Pursuit Evasion on Graphs

We introduce and study the game of "Selfish Cops and Active Robber" (SCAR) which can be seen as an multiplayer variant of the "classic" two-player Cops and Robbers (CR) game. In classic CR all cops are controlled by a single player, who has no preference over which cop captures the robber. In SCAR, on the other hand, each of N-1 cops is controlled by a separate player, and a single robber is controlled by the N-th player; and the capturing cop player receives a higher reward than the non-capturing ones. Consequently, SCAR is an N-player pursuit game on graphs, in which each cop player has an increased motive to be the one who captures the robber. The focus of our study is the existence and properties of SCAR Nash Equilibria (NE). In particular, we prove that SCAR always has one NE in deterministic positional strategies and (for N greater than two) another in deterministic nonpositional strategies. Furthermore, we study conditions which, at equilibrium, guarantee either capture or escape of the robber and show that (because of the antagonism between the "selfish" cop players) the robber may, in certain SCAR configurations, be captured later than he would be in classic CR, or even not captured at all. Finally we define the selfish cop number of a graph and study its connection to the classic cop number.

cs.DM↗

arXiv2009

Searching the Nodes of a Graph: Theory and Algorithms

One or more searchers must capture an invisible evader hiding in the nodes of a graph. We study this graph search problem; we emphasize that we study the capture of a node-located evader, which has received less attention than edge search. We show that in general graphs the problem of node search is easier than that of edge search (however node search is NP-complete, just like edge search). We concentrate on the internal monotone connected (IMC) node search of trees and show that it is essentially equivalent to IMC edge search. For IMC node search on general graphs we present a new algorithm: GSST (Guaranteed Search by Spanning Tree) which clears the graph G by performing all its clearing moves along a spanning tree T of G. We prove the existence of probabilistically complete variants of GSST. Our experiments also indicate that GSST can efficiently node-clear large graphs given only a small running time. An implementation of GSST is also provided and made publicly available.

cs.DM↗

arXiv2003

The Liar and Related Paradoxes: Fuzzy Truth Value Assignment for Collections of Self-Referential Sentences

We study self-referential sentences of the type related to the Liar paradox. In particular, we consider the problem of assigning consistent fuzzy truth values to collections of self-referential sentences. We show that the problem can be reduced to the solution of a system of nonlinear equations. Furthermore, we prove that, under mild conditions, such a system always has a solution (i.e. a consistent truth value assignment) and that, for a particular implementation of logical ``and'', ``or'' and ``negation'', the ``mid-point'' solution is always consistent. Next we turn to computational issues and present several truth-value assignment algorithms; we argue that these algorithms can be understood as generalized sequential reasoning. In an Appendix we present a large number of examples of self-referential collections (including the Liar and the Strengthened Liar), we formulate the corresponding truth value equations and solve them analytically and/ or numerically.

cs.LO↗

arXiv2003

Multi-valued Connectives for Fuzzy Sets

We present a procedure for the construction of multi-valued t-norms and t-conorms. Our procedure makes use of a pair of single-valued t-norms and the respective dual t-conorms and produces interval-valued t-norms and t-conorms. In this manner we combine desirable characteristics of different t-norms and t-conorms; if we use the t-norm min and t-conorm max, then the resulting structure is a superlattice, i.e. the multivalued analog of a lattice.

cs.OH↗

arXiv2002

Hidden Markov model segmentation of hydrological and enviromental time series

Motivated by Hubert's segmentation procedure we discuss the application of hidden Markov models (HMM) to the segmentation of hydrological and enviromental time series. We use a HMM algorithm which segments time series of several hundred terms in a few seconds and is computationally feasible for even longer time series. The segmentation algorithm computes the Maximum Likelihood segmentation by use of an expectation / maximization iteration. We rigorously prove algorithm convergence and use numerical experiments, involving temperature and river discharge time series, to show that the algorithm usually converges to the globally optimal segmentation. The relation of the proposed algorithm to Hubert's segmentation procedure is also discussed.

cs.CE↗

arXiv2002

The Lattice of Fuzzy Intervals and Sufficient Conditions for its Distributivity

Given a reference lattice, we define fuzzy intervals to be the fuzzy sets such that their p-cuts are crisp closed intervals. We show that: given a complete reference lattice, the collection of its fuzzy intervals is a complete lattice. Furthermore we show that: if the reference lattice is completely distributive then the lattice of its fuzzy intervals is distributive.

cs.OH↗

arXiv2001

L-Fuzzy Valued Inclusion Measure, L-Fuzzy Similarity and L-Fuzzy Distance

The starting point of this paper is the introduction of a new measure of inclusion of fuzzy set A in fuzzy set B. Previously used inclusion measures take values in the interval [0,1]; the inclusion measure proposed here takes values in a Boolean lattice. In other words, inclusion is viewed as an L-fuzzy valued relation between fuzzy sets. This relation is re exive, antisymmetric and transitive, i.e. it is a fuzzy order relation; in addition it possesess a number of properties which various authors have postulated as axiomatically appropriate for an inclusion measure. We also define an L-fuzzy valued measure of similarity between fuzzy sets and and an L-fuzzy valued distance function between fuzzy sets; these possess properties analogous to the ones of real-valued similarity and distance functions. Keywords: Fuzzy Relations, inclusion measure, subsethood, L-fuzzy sets, similarity, distance, transitivity.

cs.OH↗