Issa Hanou

Issa Hanou, Eric Kemmeren, Devin Wild Thomas et al.

Executing a multi-agent plan can be challenging when an agent is delayed, because this typically creates conflicts with other agents. So, we need to quickly find a new safe plan. Replanning only the delayed agent often does not result in an efficient plan, and sometimes cannot even yield a feasible plan. On the other hand, replanning other agents may lead to a cascade of changes and delays. We show how to efficiently replan by tracking and using the temporal flexibility of other agents while avoiding cascading delays. This flexibility is the maximum delay an agent can take without changing the order of or further delaying more agents. Our algorithm, FlexSIPP, precomputes all possible plans for the delayed agent, also returning the changes for the other agents, for any single-agent delay within the given scenario. We demonstrate our method in a real-world case study of replanning trains in the densely-used Dutch railway network. Our experiments show that FlexSIPP provides effective solutions, relevant to real-world adjustments, and within a reasonable timeframe.

Tilman Hinnerichs, Reuben Gardos Reid, Jaap de Jong et al.

Program synthesis -- the automatic generation of code given a specification -- is one of the most fundamental tasks in artificial intelligence (AI) and many programmers' dream. Numerous synthesizers have been developed to tackle program synthesis, manifesting different ideas to approach the exponentially growing program space. While numerous smart program synthesis tools exist, reusing and remixing previously developed methods is tedious and time-consuming. We propose Herb.jl, a unifying program synthesis library written in the Julia programming language, to address these issues. Since current methods rely on similar building blocks, we aim to modularize the underlying synthesis algorithm into communicating and fully extendable sub-compartments, allowing for straightforward reapplication of these modules. To demonstrate the benefits of using Herb.jl, we show three common use cases: 1. how to implement a simple problem and grammar, and how to solve it, 2. how to implement a previously developed synthesizer with just a few lines of code, and 3. how to run a synthesizer against a benchmark.

Issa Hanou, Sebastijan Dumančić, Mathijs de Weerdt

We propose a new framework for discovering landmarks that automatically generalize across a domain. These generalized landmarks are learned from a set of solved instances and describe intermediate goals for planning problems where traditional landmark extraction algorithms fall short. Our generalized landmarks extend beyond the predicates of a domain by using state functions that are independent of the objects of a specific problem and apply to all similar objects, thus capturing repetition. Based on these functions, we construct a directed generalized landmark graph that defines the landmark progression, including loop possibilities for repetitive subplans. We show how to use this graph in a heuristic to solve new problem instances of the same domain. Our results show that the generalized landmark graphs learned from a few small instances are also effective for larger instances in the same domain. If a loop that indicates repetition is identified, we see a significant improvement in heuristic performance over the baseline. Generalized landmarks capture domain information that is interpretable and useful to an automated planner. This information can be discovered from a small set of plans for the same domain.