Dynamic Controllability and Dispatchability Relationships

Morris, Paul

doi:10.1007/978-3-319-07046-9_33

Cited by 51 publications

(81 citation statements)

References 9 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Conflict-directed search is a generalized technique for efficiently pruning the remaining search space, but to work it needs a way to extract conflicts from an infeasible problem that explains why the problem was infeasible [Williams and Ragno, 2007]. To that end, we augment the best known O(n 3 ) dynamic controllability checking algorithm [Morris, 2014] to output conflicts to be used in conflictdirected search. This represents an improvement over the O(n 4 ) runtime for the best available algorithm for generating conflicts for dynamic controllability .…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Faster Conflict Generation for Dynamic Controllability

Bhargava

Vaquero

Williams

2017

Proceedings of the Twenty-Sixth International Joint Conference on Artificial Intelligence

View full text Add to dashboard Cite

In this paper, we focus on speeding up the temporal plan relaxation problem for dynamically controllable systems. We take a look at the current bestknown algorithm for determining dynamic controllability and augment it to efficiently generate conflicts when the network is deemed uncontrollable. Our work preserves the O(n 3 ) runtime of the best available dynamic controllability checker and improves on the previous best runtime of O(n 4 ) for extracting dynamic controllability conflicts. We then turn our attention to temporal plan relaxation tasks and show how we can leverage our work on conflicts and the structure of the network to efficiently make incremental updates intended to restore dynamic controllability by relaxing constraints. Our new algorithm, RELAXIDC, has the same asymptotic runtime as previous algorithms but sees dramatic empirical improvements over the course of repeated dynamic controllability checks.

show abstract

Section: Introductionmentioning

confidence: 99%

“…Morris [2006] introduces a series of reductions that can be applied to a labeled distance graph that preserve these relations and extends them to derive new constraints beyond those originally specified in the STNU. These were later updated in [Morris, 2014] and are reproduced below:…”

Section: Introductionmentioning

confidence: 99%

Faster Conflict Generation for Dynamic Controllability

Bhargava

Vaquero

Williams

2017

Proceedings of the Twenty-Sixth International Joint Conference on Artificial Intelligence

View full text Add to dashboard Cite

show abstract

“…Recently an algorithm for full DC verification which is O(n 3 ) was published by Morris [18]. We wish to clarify the relation between this work and his.…”

Section: Related and Future Workmentioning

confidence: 94%

“…c) The dispatcher chooses to execute node 2 at time 8 which leads to a propagation of tighter bounds to node 3. The new bounds become [13,18] but node 3 does not become enabled.…”

Section: Notationmentioning

confidence: 99%

See 1 more Smart Citation

Efficient Temporal Reasoning with Uncertainty

Nilsson¹

2015

View full text Add to dashboard Cite

Automated Planning is an active area within Artificial Intelligence. With the help of computers we can quickly find good plans in complicated problem domains, such as planning for search and rescue after a natural disaster. When planning in realistic domains the exact duration of an action generally cannot be predicted in advance. Temporal planning therefore tends to use upper bounds on durations, with the explicit or implicit assumption that if an action happens to be executed more quickly, the plan will still succeed. However, this assumption is often false. If we finish cooking too early, the dinner will be cold before everyone is at home and can eat. Simple Temporal Networks with Uncertainty (STNUs) allow us to model such situations. An STNU-based planner must verify that the temporal problems it generates are executable, which is captured by the property of dynamic controllability (DC). If a plan is not dynamically controllable, adding actions cannot restore controllability. Therefore a planner should verify after each action addition whether the plan remains DC, and if not, backtrack. Verifying dynamic controllability of a full STNU is computationally intensive. Therefore, incremental DC verification algorithms are needed.We start by discussing two existing algorithms relevant to the thesis. These are the very first DC verification algorithm called MMV (by Morris, Muscettola and Vidal) and the incremental DC verification algorithm called FastIDC, which is based on MMV.We then show that FastIDC is not sound, sometimes labeling networks as dynamically controllable when they are not. We analyze the algorithm to pinpoint the cause and show how the algorithm can be modified to correctly and efficiently detect uncontrollable networks.In the next part we use insights from this work to re-analyze the MMV algorithm. This algorithm is pseudo-polynomial and was later subsumed by first an O(n 5 ) algorithm and then an O(n 4 ) algorithm. We show that the basic techniques used by MMV can in fact be used to create an O(n 4 ) algorithm for verifying dynamic controllability, with a new termination criterion based on a deeper analysis of MMV. This means that there is now a comparatively easy way of implementing a highly efficient dynamic controllability verification algorithm. From a theoretical viewpoint, understanding MMV is important since it acts as a building block for all subsequent algorithms that verify dynamic controllability. In our analysis we also discuss a change in MMV which reduces the amount of regression needed in the network substantially.In the final part of the thesis we show that the FastIDC method can result in traversing part of a temporal network multiple times, with constraints slowly tightening towards their final values. As a result of our analysis we then present a new algorithm with an improved traversal strategy that avoids this behavior. The new algorithm, EfficientIDC, has a time complexity which is lower than that of FastIDC. We prove that it is sound and complete.This research work ...

show abstract