STATE-SPACE PLANNING WITH VARIANTS OF A*

2006 ◽  
Vol 15 (03) ◽  
pp. 433-464 ◽  
Author(s):  
AMOL DATTATRAYA MALI ◽  
MINH TANG
Keyword(s):  
State Space ◽  
Heuristic Search ◽  
Empirical Evaluation ◽  
Heuristic Evaluation ◽  
Lazy Evaluation ◽  
Two Phase ◽  
Space Planning ◽  
Future Work ◽  
Phase Evaluation ◽  
Domain Independent

Significant advances have occurred in heuristic search for planning in the last eleven years. Many of these planners use A*-style search. We report on five sound and complete domain-independent forward state-space STRIPS planners in this paper. The planners are AWA* (Adjusted Weighted A*), MAWA* (Modified AWA*), AWA*-AC (AWA* with action conflict-based adjustment), AWA*-PD (AWA* with deleted preconditions-based adjustment), and AWA*-AC-LE (AWA*-AC with lazy evaluation). AWA* is the first planner to use node-dependent weighting in A*. MAWA*, AWA*-AC, AWA*-PD, and AWA*-AC-LE use conditional two-phase heuristic evaluation. MAWA* applies node-dependent weighting to a subset of the nodes in the fringe, after the two-phase evaluation. One novel idea in AWA*-AC-LE is lazy heuristic evaluation which does not construct relaxed plans to compute heuristic values for all nodes. We report on an empirical comparison of AWA*, MAWA*, AWA*-AC, AWA*-PD, and AWA*-AC-LE with classical planners AltAlt, FF, HSP-2 and STAN 4. Our variants of A* outperform these planners on several problems. The empirical evaluation shows that heuristic search planning is significantly benefitted by node-dependent weighting, conditional two-phase heuristic evaluation and lazy evaluation. We report on the insights about inferior performance of our planners in some domains using the notion of waiting time. We discuss many other variants of A*, state-space planners and directions for future work.

Heuristics for Domain-Independent Planning: A Survey

2011 ◽  
Vol 135-136 ◽  
pp. 573-577 ◽  
Author(s):  
Rui Shi Liang ◽  
Min Huang
Keyword(s):  
State Space ◽  
Heuristic Search ◽  
Research Work ◽  
Future Research ◽  
Survey Analysis ◽  
Work Related ◽  
State Space Search ◽  
Survey Results ◽  
Domain Independent ◽  
Intense Research

Increasing interest has been devoted to Planning as Heuristic Search over the years. Intense research has focused on deriving fast and accurate heuristics for domain-independent planning. This paper reports on an extensive survey and analysis of research work related to heuristic derivation techniques for state space search. Survey results reveal that heuristic techniques have been extensively applied in many efficient planners and result in impressive performances. We extend the survey analysis to suggest promising avenues for future research in heuristic derivation and heuristic search techniques.

scholarly journals The GRT Planning System: Backward Heuristic Construction in Forward State-Space Planning

2001 ◽  
Vol 15 ◽  
pp. 115-161 ◽  
Author(s):  
I. Refanidis ◽  
I. Vlahavas
Keyword(s):  
State Space ◽  
Intermediate State ◽  
Forward Direction ◽  
Planning System ◽  
Search Process ◽  
Space Planning ◽  
Two Phases ◽  
Performance Results ◽  
Domain Independent ◽  
State Space Planning

This paper presents GRT, a domain-independent heuristic planning system for STRIPS worlds. GRT solves problems in two phases. In the pre-processing phase, it estimates the distance between each fact and the goals of the problem, in a backward direction. Then, in the search phase, these estimates are used in order to further estimate the distance between each intermediate state and the goals, guiding so the search process in a forward direction and on a best-first basis. The paper presents the benefits from the adoption of opposite directions between the preprocessing and the search phases, discusses some difficulties that arise in the pre-processing phase and introduces techniques to cope with them. Moreover, it presents several methods of improving the efficiency of the heuristic, by enriching the representation and by reducing the size of the problem. Finally, a method of overcoming local optimal states, based on domain axioms, is proposed. According to it, difficult problems are decomposed into easier sub-problems that have to be solved sequentially. The performance results from various domains, including those of the recent planning competitions, show that GRT is among the fastest planners.

Improving Domain-Independent Heuristic State-Space Planning via plan cost predictions

2021 ◽  
pp. 1-27
Author(s):  
Francesco Percassi ◽  
Alfonso E. Gerevini ◽  
Enrico Scala ◽  
Ivan Serina ◽  
Mauro Vallati
Keyword(s):  
State Space ◽  
Space Planning ◽  
Domain Independent ◽  
State Space Planning

scholarly journals Deterministic Oversubscription Planning as Heuristic Search: Abstractions and Reformulations

2015 ◽  
Vol 52 ◽  
pp. 97-169 ◽  
Author(s):  
Carmel Domshlak ◽  
Vitaly Mirkis
Keyword(s):  
Heuristic Search ◽  
Lower Cost ◽  
Empirical Evaluation ◽  
Search Space ◽  
Optimal Planning ◽  
Approximation Techniques ◽  
Total Action ◽  
Effective Domain ◽  
Domain Independent ◽  
Made In

While in classical planning the objective is to achieve one of the equally attractive goal states at as low total action cost as possible, the objective in deterministic oversubscription planning (OSP) is to achieve an as valuable as possible subset of goals within a fixed allowance of the total action cost. Although numerous applications in various fields share the latter objective, no substantial algorithmic advances have been made in deterministic OSP. Tracing the key sources of progress in classical planning, we identify a severe lack of effective domain-independent approximations for OSP. With our focus here on optimal planning, our goal is to bridge this gap. Two classes of approximation techniques have been found especially useful in the context of optimal classical planning: those based on state-space abstractions and those based on logical landmarks for goal reachability. The question we study here is whether some similar-in-spirit, yet possibly mathematically different, approximation techniques can be developed for OSP. In the context of abstractions, we define the notion of additive abstractions for OSP, study the complexity of deriving effective abstractions from a rich space of hypotheses, and reveal some substantial, empirically relevant islands of tractability. In the context of landmarks, we show how standard goal-reachability landmarks of certain classical planning tasks can be compiled into the OSP task of interest, resulting in an equivalent OSP task with a lower cost allowance, and thus with a smaller search space. Our empirical evaluation confirms the effectiveness of the proposed techniques, and opens a wide gate for further developments in oversubscription planning.

scholarly journals RE-DESIGN OF A MOTORCYCLE HELMET FOR USE IN URBAN TRAFFIC: CONCEPTUAL DESIGN AND TESTING

2021 ◽  
Vol 1 ◽  
pp. 2531-2540
Author(s):  
Joanna Papadopoulou ◽  
Vassilis Papakostopoulos ◽  
Vassilis C. Moulianitis
Keyword(s):  
Urban Traffic ◽  
Von Mises Stress ◽  
Two Phase ◽  
Design Concepts ◽  
Motorcycle Helmet ◽  
Maximum Protection ◽  
Von Mises ◽  
Full Face ◽  
Phase Evaluation ◽  
Design And Testing

AbstractThis paper presents the re-design approach of an urban motorcycle helmet to prevent users bypassing the strap fastening system. Related studies show that although a full-face helmet provides the maximum protection to a rider, in practice, full-face helmeted riders in urban traffic tend to improperly fasten it. On that notion, the design goal was to conceive a helmet that combines the advantages of different helmet types while responding to urban driving needs. During design ideation possible solutions were examined focusing on different ways of accessing and fixating the helmet on a rider’s head, without using a strap fastening system. Preliminary concept development produced three design concepts, that were evaluated using two sets of prototypes: (a) the 3D printing method under a 1:2 scale was used to detect any design faults, while the 3D modeled concepts were evaluated in four different crash impacts regarding total deformation and von-Mises stress, and (b) 1:1 models of the three concepts were used by experienced riders to assess possible usability issues during helmet placement/removal. Results of the two-phase evaluation of the three concepts and design issues for further development of them are discussed.

Embedded Two-Phase Cooling of High Flux Electronics via Micro-Enabled Surfaces and Fluid Delivery Systems (FEEDS)

2015 ◽  
Author(s):  
Raphael Mandel ◽  
Serguei Dessiatoun ◽  
Patrick McCluskey ◽  
Michael Ohadi
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Saturation Temperature ◽  
Absolute Pressure ◽  
High Flux ◽  
Vapor Quality ◽  
Two Phase ◽  
Fluid Delivery ◽  
Future Work

This work presents the experimental design and testing of a two-phase, embedded manifold-microchannel cooler for cooling of high flux electronics. The ultimate goal of this work is to achieve 0.025 cm2-K/W thermal resistance at 1 kW/cm2 heat flux and evaporator exit vapor qualities at or exceeding 90% at less than 10% absolute pressure drop. While the ultimate goal is to obtain a working two-phase embedded cooler, the system was first tested in single-phase mode to validate system performance via comparison of experimentally measured heat transfer coefficient and pressure drop to the values predicted by CFD simulations. Upon validation, the system was tested in two phase mode using R245fa at 30°C saturation temperature and achieved in excess of 1 kW/cm2 heat flux at 45% vapor quality. Future work will focus on increasing the exit vapor quality as well as use of SiC for the heat transfer surface upon completion of current experiments with Si.

scholarly journals Front-to-Front Heuristic Search for Satisficing Classical Planning

2020 ◽  
Author(s):  
Ryo Kuroiwa ◽  
Alex Fukunaga
Keyword(s):  
Heuristic Search ◽  
Search Strategy ◽  
State Of The Art ◽  
Heuristic Evaluation ◽  
Bidirectional Search

Although symbolic bidirectional search is successful in optimal classical planning, state-of-the-art satisficing planners do not use bidirectional search. Previous bidirectional search planners for satisficing planning behaved similarly to a trivial portfolio, which independently executes forward and backward search without the desired ``meet-in-the-middle'' behavior of bidirectional search where the forward and backward search frontiers intersect at some point relatively far from the forward and backward start states. In this paper, we propose Top-to-Top Bidirectional Search (TTBS), a new bidirectional search strategy with front-to-front heuristic evaluation. We show that TTBS strongly exhibits ``meet-in-the-middle'' behavior and can solve instances solved by neither forward nor backward search on a number of domains.

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