Amanda Coles

A Survey of the Seventh International Planning Competition

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.

COLIN: planning with continuous linear numeric change

In this paper we describe COLIN, a forward-chaining heuristic search planner, capable of reasoning with COntinuous LINear numeric change, in addition to the full temporal semantics of PDDL2.1. Through this work we make two advances to the state-of-the-art in terms of expressive reasoning capabilities of planners: the handling of continuous linear change, and the handling of duration-dependent effects in combination with duration inequalities, both of which require tightly coupled temporal and numeric reasoning during planning. COLIN combines FF-style forward chaining search, with the use of a Linear Program (LP) to check the consistency of the interacting temporal and numeric constraints at each state. The LP is used to compute bounds on the values of variables in each state, reducing the range of actions that need to be considered for application. In addition, we develop an extension of the Temporal Relaxed Planning Graph heuristic of CRIKEY3, to support reasoning directly with continuous change. We extend the range of task variables considered to be suitable candidates for specifying the gradient of the continuous numeric change effected by an action. Finally, we explore the potential for employing mixed integer programming as a tool for optimising the timestamps of the actions in the plan, once a solution has been found. To support this, we further contribute a selection of extended benchmark domains that include continuous numeric effects. We present results for COLIN that demonstrate its scalability on a range of benchmarks, and compare to existing state-of-the-art planners.

A hybrid LP-RPG heuristic for modelling numeric resource flows in planning

Although the use of metric fluents is fundamental to many practical planning problems, the study of heuristics to support fully automated planners working with these fluents remains relatively unexplored. The most widely used heuristic is the relaxation of metric fluents into interval-valued variables --- an idea first proposed a decade ago. Other heuristics depend on domain encodings that supply additional information about fluents, such as capacity constraints or other resource-related annotations. A particular challenge to these approaches is in handling interactions between metric fluents that represent exchange, such as the transformation of quantities of raw materials into quantities of processed goods, or trading of money for materials. The usual relaxation of metric fluents is often very poor in these situations, since it does not recognise that resources, once spent, are no longer available to be spent again. We present a heuristic for numeric planning problems building on the propositional relaxed planning graph, but using a mathematical program for numeric reasoning. We define a class of producer--consumer planning problems and demonstrate how the numeric constraints in these can be modelled in a mixed integer program (MIP). This MIP is then combined with a metric Relaxed Planning Graph (RPG) heuristic to produce an integrated hybrid heuristic. The MIP tracks resource use more accurately than the usual relaxation, but relaxes the ordering of actions, while the RPG captures the causal propositional aspects of the problem. We discuss how these two components interact to produce a single unified heuristic and go on to explore how further numeric features of planning problems can be integrated into the MIP. We show that encoding a limited subset of the propositional problem to augment the MIP can yield more accurate guidance, partly by exploiting structure such as propositional landmarks and propositional resources. Our results show that the use of this heuristic enhances scalability on problems where numeric resource interaction is key in finding a solution.

Automated planning of simple persuasion dialogues

We take a simple form of non-adversarial persuasion dialogue in which one participant (the persuader) aims to convince the other (the responder) to accept the topic of the dialogue by asserting sets of beliefs. The responder replies honestly to indicate whether it finds the topic to be acceptable (we make no prescription as to what formalism and semantics must be used for this, only assuming some function for determining acceptable beliefs from a logical knowledge base). Our persuader has a model of the responder, which assigns probabilities to sets of beliefs, representing the likelihood that each set is the responder’s actual beliefs. The beliefs the persuader chooses to assert and the order in which it asserts them (i.e. its strategy) can impact on the success of the dialogue and the success of a particular strategy cannot generally be guaranteed (because of the uncertainty over the responder’s beliefs). We define our persuasion dialogue as a classical planning problem, which can then be solved by an automated planner to generate a strategy that maximises the chance of success given the persuader’s model of the responder; this allows us to exploit the power of existing automated planners, which have been shown to be efficient in many complex domains. We provide preliminary results that demonstrate how the efficiency of our approach scales with the number of beliefs.

Opportunistic branched plans to maximise utility in the presence of resource uncertainty

In many applications, especially autonomous exploration, there is a trade-off between operational safety, forcing conservatism about resource usage; and maximising utility, requiring high resource utilisation. In this paper we consider a method of generating plans that maintain this conservatism whilst allowing exploitation of situations where resource usage is better than pessimistically estimated. We consider planning problems with soft goals, each with a violation cost. The challenge is to maximise utility (minimise the violation cost paid) whilst maintaining confidence that the plan will execute within the specified limits. We first show how forward search planning can be extended to generate such plans. Then we extend this to build branched plans: tree structures labelled with conditions on executing branches. Lower cost branches can be followed if their conditions are met. We demonstrate that the use of such plans can dramatically increase utility whilst still obeying strict safety constraints.

Automated Planning of Simple Persuasion Dialogues

We take a simple form of non-adversarial persuasion dialogue in which one participant (the persuader) aims to convince the other (the responder) to accept the topic of the dialogue by asserting sets of beliefs. The responder replies honestly to indicate whether it finds the topic to be acceptable (we make no prescription as to what formalism and semantics must be used for this, only assuming some function for determining acceptable beliefs from a logical knowledge base). Our persuader has a model of the responder, which assigns probabilities to sets of beliefs, representing the likelihood that each set is the responder’s actual beliefs. The beliefs the persuader chooses to assert and the order in which it asserts them (i.e. its strategy) can impact on the success of the dialogue and the success of a particular strategy cannot generally be guaranteed (because of the uncertainty over the responder’s beliefs). We define our persuasion dialogue as a classical planning problem, which can then be solved by an automated planner to generate a strategy that maximises the chance of success given the persuader’s model of the responder; this allows us to exploit the power of existing automated planners, which have been shown to be efficient in many complex domains. We provide preliminary results that demonstrate how the efficiency of our approach scales with the number of beliefs.

Optimal simple strategies for persuasion

Citation for published version (APA): Black, E., Coles, A., & Hampson, C. (2016). Optimal simple strategies for persuasion. In Frontiers in Artificial Intelligence and Applications: 22nd European Conference on Artificial Intelligence 29 August–2 September 2016, The Hague, The Netherlands (Vol. 285, pp. 1736-1737). (Frontiers in Artificial Intelligence and Applications; Vol. 285). IOS Press. DOI: 10.3233/978-1-61499-672-9-1736

Computational Logic in Multi-Agent Systems

We take a simple form of non-adversarial persuasion dialogue in which one participant (the persuader) aims to convince the other (the responder) to accept the topic of the dialogue by asserting sets of beliefs. The responder replies honestly to indicate whether it finds the topic to be acceptable (we make no prescription as to what formalism and semantics must be used for this, only assuming some function for determining acceptable beliefs from a logical knowledge base). Our persuader has a model of the responder, which assigns probabilities to sets of beliefs, representing the likelihood that each set is the responder’s actual beliefs. The beliefs the persuader chooses to assert and the order in which it asserts them (i.e. its strategy) can impact on the success of the dialogue and the success of a particular strategy cannot generally be guaranteed (because of the uncertainty over the responder’s beliefs). We define our persuasion dialogue as a classical planning problem, which can then be solved by an automated planner to generate a strategy that maximises the chance of success given the persuader’s model of the responder; this allows us to exploit the power of existing automated planners, which have been shown to be efficient in many complex domains. We provide preliminary results that demonstrate how the efficiency of our approach scales with the number of beliefs.