Planning & Scheduling: Overviews

The reactive multiple operating room surgical case sequencing problem Artificial Intelligence

In this paper we consider the surgical case sequencing problem (SCSP) under stochastic conditions. In addition to implementing a robust surgical schedule, we investigate the use of a number of reactive strategies that can be used to maintain schedule feasibility. We present a mixed integer nonlinear programming (MINLP) model for the reactive multiple operating room (OR) SCSP that may be suitable for direct implementation on small problem instances. A machine scheduling perspective is considered and the model is equivalent to a resource-constrained parallel-machine scheduling problem with identical machines, machine eligibility restrictions, and machine and job release dates. The explicit objective of the model is to reduce OR idle time, although other common objectives (including time to surgery and overtime) are discussed. The work here is based on a case study of a large Australian public hospital with long surgical waiting lists and high non-elective demand. Results of computational experiments show that the reactive strategies presented in this paper can be used to reduce idle time without putting excessive pressure on surgeons.

The real-time reactive surgical case sequencing problem Artificial Intelligence

In this paper, the multiple operating room (OR) surgical case sequencing problem (SCSP) is addressed. The objective is to maximise total OR utilisation during standard opening hours. The work here is based on a case study of a large Australian public hospital with long surgical waiting lists and high levels of non-elective demand. Due to the complexity of the SCSP and the size of the instances considered herein, heuristic techniques are required to solve the problem. Constructive heuristics are presented based on both a modified block scheduling policy and an open scheduling policy. A number of real-time reactive strategies are presented that can be used to maintain schedule feasibility in the case of disruptions. Results of computational experiments show that the approach presented in this paper can be used to maintain schedule feasibility in real-time, whilst increasing OT utilisation and throughput, and reducing the waiting time of non-elective patients. The framework presented here is applicable to the real-life scheduling of OT departments, and recommendations have been provided regarding implementation of the approach.

A Hybrid Genetic Algorithm for Parallel Machine Scheduling at Semiconductor Back-End Production

AAAI Conferences

This paper addresses batch scheduling at a back-end semiconductor plant of Nexperia. This complex manufacturing environment is characterized by a large product and batch size variety, numerous parallel machines with large capacity differences, sequence and machine dependent setup times and machine eligibility constraints. A hybrid genetic algorithm is proposed to improve the scheduling process, the main features of which are a local search enhanced crossover mechanism, two additional fast local search procedures and a user-controlled multi-objective fitness function. Testing with real-life production data shows that this multi-objective approach can strike the desired balance between production time, setup time and tardiness, yielding high-quality practically feasible production schedules.

Monte-Carlo Planning for Agile Legged Locomotion

AAAI Conferences

Recent progress in legged locomotion research has produced robots that can perform agile blind-walking with robustness comparable to a blindfolded human. However, this walking approach has not yet been integrated with planners for high-level activities. In this paper, we take a step towards high-level task planning for these robots by studying a planar simulated biped that captures their essential dynamics. We investigate variants of Monte-Carlo Tree Search (MCTS) for selecting an appropriate blind-walking controller at each decision cycle. In particular, we consider UCT with an intelligently selected rollout policy, which is shown to be capable of guiding the biped through treacherous terrain. In addition, we develop a new MCTS variant, called Monte-Carlo Discrepancy Search (MCDS), which is shown to make more effective use of limited planning time than UCT for this domain. We demonstrate the effectiveness of these planners in both deterministic and stochastic environments across a range of algorithm parameters. In addition, we present results for using these planners to control a full-order 3D simulation of Cassie, an agile bipedal robot, through complex terrain.

Towards Explainable NPCs: A Relational Exploration Learning Agent

AAAI Conferences

Non-player characters (NPCs) in video games are a common form of frustration for players because they generally provide no explanations for their actions or provide simplistic explanations using fixed scripts. Motivated by this, we consider a new design for agents that can learn about their environments, accomplish a range of goals, and explain what they are doing to a supervisor. We propose a framework for studying this type of agent, and compare it to existing reinforcement learning and self-motivated agent frameworks. We propose a novel design for an initial agent that acts within this framework. Finally, we describe an evaluation centered around the supervisor's satisfaction and understanding of the agent's behavior.

Probabilistic Planning by Probabilistic Programming

AAAI Conferences

Automated planning is a major topic of research in artificial intelligence, and enjoys a long and distinguished history. The classical paradigm assumes a distinguished initial state, comprised of a set of facts, and is defined over a set of actions which change that state in one way or another. Planning in many real-world settings, however, is much more involved: an agent's knowledge is almost never simply a set of facts that are true, and actions that the agent intends to execute never operate the way they are supposed to. Thus, probabilistic planning attempts to incorporate stochastic models directly into the planning process. In this article, we briefly report on probabilistic planning through the lens of probabilistic programming: a programming paradigm that aims to ease the specification of structured probability distributions. In particular, we provide an overview of the features of two systems, HYPE and ALLEGRO, which emphasise different strengths of probabilistic programming that are particularly useful for complex modelling issues raised in probabilistic planning. Among other things, with these systems, one can instantiate planning problems with growing and shrinking state spaces, discrete and continuous probability distributions, and non-unique prior distributions in a first-order setting.

A Survey of the Seventh International Planning Competition

AI Magazine

In this article we review the 2011 International Planning Competition. We give an overview of the history of the competition, discussing how it has developed since its first edition in 1998. The 2011 competition was run in three main separate tracks: the deterministic (classical) track; the learning track; and the uncertainty track. Each track proposed its own distinct set of new challenges and the participants rose to these admirably, the results of each track showing promising progress in each area. The competition attracted a record number of participants this year, showing its continued and strong position as a major central pillar of the international planning research community.

A Survey of Research in Distributed, Continual Planning

AI Magazine

Complex, real-world domains require rethinking traditional approaches to AI planning. Planning and executing the resulting plans in a dynamic environment implies a continual approach in which planning and execution are interleaved, uncertainty in the current and projected world state is recognized and handled appropriately, and replanning can be performed when the situation changes or planned actions fail. Furthermore, complex planning and execution problems may require multiple computational agents and human planners to collaborate on a solution. In this article, we describe a new paradigm for planning in complex, dynamic environments, which we term distributed, continual planning (DCP). We argue that developing DCP systems will be necessary for planning applications to be successful in these environments.