title: Phase transition in the countdown problem.
abstract: We present a combinatorial decision problem, inspired by the celebrated quiz show called Countdown, that involves the computation of a given target number T from a set of k randomly chosen integers along with a set of arithmetic operations. We find that the probability of winning the game evidences a threshold phenomenon that can be understood in the terms of an algorithmic phase transition as a function of the set size k. Numerical simulations show that such probability sharply transitions from zero to one at some critical value of the control parameter, hence separating the algorithm's parameter space in different phases. We also find that the system is maximally efficient close to the critical point. We derive analytical expressions that match the numerical results for finite size and permit us to extrapolate the behavior in the thermodynamic limit.
authors.affiliation: Departamento de Matemática Aplicada y Estadística, Escuela Técnica Superior de Ingenieros Aeronáuticos, Universidad Politécnica de Madrid, 28040 Madrid, Spain. lucas.lacasa@upm.es
authors.forename: Lucas
authors.initials: L
authors.lastname: Lacasa
authors.forename: Bartolo
authors.initials: B
authors.lastname: Luque
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D015233:Models, Statistical; D044367:Phase Transition; D013816:Thermodynamics