We consider reinforcement learning (RL) in Markov Decision Processes (MDPs) in which at each time step the agent, in addition to earning a reward, also incurs an $M$ dimensional vector of costs. The objective is to design a learning rule that maximizes the cumulative reward earned over a finite time horizon of $T$ steps, while simultaneously ensuring that the cumulative cost expenditures are bounded appropriately. The considerations on the cumulative cost expenditures is in departure from the existing RL literature, in that the agent now additionally needs to balance the cost expenses in an \emph{online manner}, while simultaneously performing optimally the exploration-exploitation trade-off typically encountered in RL tasks. This is challenging since either of the duo objectives of exploration and exploitation necessarily require the agent to expend resources. When the constraints are placed on the average costs, we present a version of UCB algorithm and prove that its reward as well as cost regrets are upper-bounded as $O\left(T_{M}S\sqrt{AT\log(T)}\right)$, where $T_{M}$ is the mixing time of the MDP, $S$ is the number of states, $A$ is the number of actions, and $T$ is the time horizon. We further show how to modify the algorithm in order to reduce regrets of a desired subset of the $M$ costs, at the expense of increasing the regrets of rewards and the remaining costs. We then consider RL under the constraint that the vector comprising of the cumulative cost expenditures until each time $t\le T$ must be less than $\mathbf{c}^{ub}t$. We propose a "finite ($B$)-state" algorithm and show that its average reward is within $O\left(e^{-B}\right)$ of $r^{\star}$, the latter being the optimal average reward under average cost constraints.

本文研究如何在满足成本平均值约束条件下，通过设计基于模型的强化学习算法，从而最大化累积奖励，同时确保每个成本值的平均值被绑定在特定的上界之内。此外，我们提出了一种衡量强化学习算法表现的方法，即使用M+1维的后悔向量来衡量奖励和不同成本的差异，并证明了UCRL-CMDP算法的后悔向量的期望值的上界为O（T ^ {2/3}）.

在约束条件下的马尔可夫决策过程学习