U??; . . . ; u U ?g refers to its finite action space. When the MDP is in state xt at time t and action ut is selected, the agent moves instantaneously to a next state xt+1 with a probability of P(xt+1|xt, ut) = f(xt, ut, xt+1). An instantaneous deterministic, bounded reward rt = M(xt, ut, xt+1) 2 [Rmin, Rmax] is observed.PLOS ONE | DOI:10.1371/journal.pone.0157088 June 15,2 /Benchmarking for Bayesian Reinforcement LearningLet ht = (x0, u0, r0, x1, ??? xt – 1, ut – 1, rt – 1, xt) 2 H denote the history observed until time t. An E/E strategy is a stochastic policy which, given the current history ht, returns an action ut * (ht). Given a probability distribution over initial states pM, 0(?, the expected return of a given E/E strategy with respect to the MDP M can be defined as follows:p JM ?x0 pM;0 ?Ep 0 ? Mwhere Rp 0 ?is the stochastic sum of PD98059 biological activity discounted rewards received when applying the policy M , starting from an initial state x0: Rp 0 ??M? X t? p RL aims to learn the behaviour that maximises JM , i.e. learning a policy ?defined as follows:gt rt :p?2 arg maxpp JM :2.2 Prior KnowledgeIn this paper, the actual MDP is assumed to be unknown. Model-based Bayesian Reinforcement Learning (BRL) proposes to the model the uncertainty, using a probability distribution p0 ?over a set of candidate MDPs M. Such a probability distribution is called a prior distriM bution and can be used to encode specific prior knowledge available before interaction. Given a prior distribution p0 ? the expected return of a given E/E strategy is defined as: M ?p?JM ; Jp0 ??E pMM pM?In the BRL framework, the goal is to maximise Jp0 p optimal policy” and defined as follows: p?2 arg maxpM?, by finding ?, which is called “Bayesian Jp0 p :M?2.3 RP54476MedChemExpress Dalfopristin computation time characterisationMost BRL algorithms rely on some properties which, given sufficient computation time, ensure that their agents will converge to an optimal behaviour. However, it is not clear to know beforehand whether an algorithm will satisfy fixed computation time constraints while providing good performances. The parameterisation of the algorithms makes the selection even more complex. Most BRL algorithms depend on parameters (number of transitions simulated at each iteration, etc.) which, in some way, can affect the computation time. In addition, for one given algorithm and fixed parameters, the computation time often varies from one simulation to another. These features make it nearly impossible to compare BRL algorithms under strict computation time constraints. In this paper, to address this problem, algorithms are run with multiple choices of parameters, and we analyse their time performance a posteriori. Furthermore, a distinction between the offline and online computation time is made. Offline computation time corresponds to the moment when the agent is able to exploit its prior knowledge, but cannot interact with the MDP yet. One can see it as the time given to take the first decision. In most algorithms concerned in this paper, this phase is generally used to initialise some data structure. On the other hand, online computation time corresponds to the time consumed by an algorithm for taking each decision.PLOS ONE | DOI:10.1371/journal.pone.0157088 June 15,3 /Benchmarking for Bayesian Reinforcement LearningThere are many ways to characterise algorithms based on their computation time. One can compare them based on the average time needed per step or on the offline computation time alone. To re.U??; . . . ; u U ?g refers to its finite action space. When the MDP is in state xt at time t and action ut is selected, the agent moves instantaneously to a next state xt+1 with a probability of P(xt+1|xt, ut) = f(xt, ut, xt+1). An instantaneous deterministic, bounded reward rt = M(xt, ut, xt+1) 2 [Rmin, Rmax] is observed.PLOS ONE | DOI:10.1371/journal.pone.0157088 June 15,2 /Benchmarking for Bayesian Reinforcement LearningLet ht = (x0, u0, r0, x1, ??? xt – 1, ut – 1, rt – 1, xt) 2 H denote the history observed until time t. An E/E strategy is a stochastic policy which, given the current history ht, returns an action ut * (ht). Given a probability distribution over initial states pM, 0(?, the expected return of a given E/E strategy with respect to the MDP M can be defined as follows:p JM ?x0 pM;0 ?Ep 0 ? Mwhere Rp 0 ?is the stochastic sum of discounted rewards received when applying the policy M , starting from an initial state x0: Rp 0 ??M? X t? p RL aims to learn the behaviour that maximises JM , i.e. learning a policy ?defined as follows:gt rt :p?2 arg maxpp JM :2.2 Prior KnowledgeIn this paper, the actual MDP is assumed to be unknown. Model-based Bayesian Reinforcement Learning (BRL) proposes to the model the uncertainty, using a probability distribution p0 ?over a set of candidate MDPs M. Such a probability distribution is called a prior distriM bution and can be used to encode specific prior knowledge available before interaction. Given a prior distribution p0 ? the expected return of a given E/E strategy is defined as: M ?p?JM ; Jp0 ??E pMM pM?In the BRL framework, the goal is to maximise Jp0 p optimal policy” and defined as follows: p?2 arg maxpM?, by finding ?, which is called “Bayesian Jp0 p :M?2.3 Computation time characterisationMost BRL algorithms rely on some properties which, given sufficient computation time, ensure that their agents will converge to an optimal behaviour. However, it is not clear to know beforehand whether an algorithm will satisfy fixed computation time constraints while providing good performances. The parameterisation of the algorithms makes the selection even more complex. Most BRL algorithms depend on parameters (number of transitions simulated at each iteration, etc.) which, in some way, can affect the computation time. In addition, for one given algorithm and fixed parameters, the computation time often varies from one simulation to another. These features make it nearly impossible to compare BRL algorithms under strict computation time constraints. In this paper, to address this problem, algorithms are run with multiple choices of parameters, and we analyse their time performance a posteriori. Furthermore, a distinction between the offline and online computation time is made. Offline computation time corresponds to the moment when the agent is able to exploit its prior knowledge, but cannot interact with the MDP yet. One can see it as the time given to take the first decision. In most algorithms concerned in this paper, this phase is generally used to initialise some data structure. On the other hand, online computation time corresponds to the time consumed by an algorithm for taking each decision.PLOS ONE | DOI:10.1371/journal.pone.0157088 June 15,3 /Benchmarking for Bayesian Reinforcement LearningThere are many ways to characterise algorithms based on their computation time. One can compare them based on the average time needed per step or on the offline computation time alone. To re.