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Akihiro Kishimoto

Possible papers associated with this exact author name in Arrow. This page groups case-insensitive exact name matches and is not a full identity disambiguation profile.

39 papers
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39

IJCAI Conference 2023 Conference Paper

An Ensemble Approach for Automated Theorem Proving Based on Efficient Name Invariant Graph Neural Representations

  • Achille Fokoue
  • Ibrahim Abdelaziz
  • Maxwell Crouse
  • Shajith Ikbal
  • Akihiro Kishimoto
  • Guilherme Lima
  • Ndivhuwo Makondo
  • Radu Marinescu

Using reinforcement learning for automated theorem proving has recently received much attention. Current approaches use representations of logical statements that often rely on the names used in these statements and, as a result, the models are generally not transferable from one domain to another. The size of these representations and whether to include the whole theory or part of it are other important decisions that affect the performance of these approaches as well as their runtime efficiency. In this paper, we present NIAGRA; an ensemble Name InvAriant Graph RepresentAtion. NIAGRA addresses this problem by using 1) improved Graph Neural Networks for learning name-invariant formula representations that is tailored for their unique characteristics and 2) an efficient ensemble approach for automated theorem proving. Our experimental evaluation shows state-of-the-art performance on multiple datasets from different domains with improvements up to 10% compared to the best learning-based approaches. Furthermore, transfer learning experiments show that our approach significantly outperforms other learning-based approaches by up to 28%.

AAAI Conference 2023 Conference Paper

Foundation Model for Material Science

  • Seiji Takeda
  • Akihiro Kishimoto
  • Lisa Hamada
  • Daiju Nakano
  • John R. Smith

Foundation models (FMs) are achieving remarkable successes to realize complex downstream tasks in domains including natural language and visions. In this paper, we propose building an FM for material science, which is trained with massive data across a wide variety of material domains and data modalities. Nowadays machine learning models play key roles in material discovery, particularly for property prediction and structure generation. However, those models have been independently developed to address only specific tasks without sharing more global knowledge. Development of an FM for material science will enable overarching modeling across material domains and data modalities by sharing their feature representations. We discuss fundamental challenges and required technologies to build an FM from the aspects of data preparation, model development, and downstream tasks.

AAAI Conference 2022 Conference Paper

Bandit Limited Discrepancy Search and Application to Machine Learning Pipeline Optimization

  • Akihiro Kishimoto
  • Djallel Bouneffouf
  • Radu Marinescu
  • Parikshit Ram
  • Ambrish Rawat
  • Martin Wistuba
  • Paulito Palmes
  • Adi Botea

Optimizing a machine learning (ML) pipeline has been an important topic of AI and ML. Despite recent progress, pipeline optimization remains a challenging problem, due to potentially many combinations to consider as well as slow training and validation. We present the BLDS algorithm for optimized algorithm selection in a fixed ML pipeline structure. BLDS performs multi-fidelity optimization for selecting ML algorithms trained with smaller computational overhead, while controlling its pipeline search based on multi-armed bandit and limited discrepancy search. Our experiments on classification benchmarks show that BLDS is superior to competing algorithms. We also combine BLDS with hyperparameter optimization, empirically showing the advantage of BLDS.

SoCS Conference 2021 Conference Paper

Counting Vertex-Disjoint Shortest Paths in Graphs

  • Adi Botea
  • Massimiliano Mattetti
  • Akihiro Kishimoto
  • Radu Marinescu 0002
  • Elizabeth M. Daly

Finding a shortest path in a graph is at the core of many combinatorial search problems. A closely related problem refers to counting the number of shortest paths between two nodes. Such problems are solvable in polynomial time in the size of the graph. However, more realistic problem formulations could additionally specify constraints to satisfy. We study the problem of counting the shortest paths that are vertex disjoint and can satisfy additional constraints. Specifically, we look at the problems of counting vertex-disjoint shortest paths in edge-colored graphs, counting vertex-disjoint shortest paths with directional constraints, and counting vertex-disjoint shortest paths between multiple source-target pairs. We give a detailed theoretical analysis, and show formally that all of these three counting problems are NP-complete in general.

AAAI Conference 2021 Conference Paper

Searching for Machine Learning Pipelines Using a Context-Free Grammar

  • Radu Marinescu
  • Akihiro Kishimoto
  • Parikshit Ram
  • Ambrish Rawat
  • Martin Wistuba
  • Paulito P. Palmes
  • Adi Botea

AutoML automatically selects, composes and parameterizes machine learning algorithms into a workflow or pipeline of operations that aims at maximizing performance on a given dataset. Although current methods for AutoML achieved impressive results they mostly concentrate on optimizing fixed linear workflows. In this paper, we take a different approach and focus on generating and optimizing pipelines of complex directed acyclic graph shapes. These complex pipeline structure may lead to discovering new synthetic features and thus boost performance considerably. We explore the power of heuristic search and context-free grammars to search and optimize these kinds of pipelines. Experiments on various benchmark datasets show that our approach is highly competitive and often outperforms existing AutoML systems.

AAAI Conference 2020 Conference Paper

Parallel AND/OR Search for Marginal MAP

  • Radu Marinescu
  • Akihiro Kishimoto
  • Adi Botea

Marginal MAP is a difficult mixed inference task for graphical models. Existing state-of-the-art algorithms for solving exactly this task are based on either depth-first or best-first sequential search over an AND/OR search space. In this paper, we explore and evaluate for the first time the power of parallel search for exact Marginal MAP inference. We introduce a new parallel shared-memory recursive best-first AND/OR search algorithm that explores the search space in a best-first manner while operating with limited memory. Subsequently, we develop a complete parallel search scheme that only parallelizes the conditional likelihood computations. We also extend the proposed algorithms into depth-first parallel search schemes. Our experiments on difficult benchmarks demonstrate the effectiveness of the parallel search algorithms against current sequential methods for solving Marginal MAP exactly.

AAAI Conference 2019 Conference Paper

Anytime Recursive Best-First Search for Bounding Marginal MAP

  • Radu Marinescu
  • Akihiro Kishimoto
  • Adi Botea
  • Rina Dechter
  • Alexander Ihler

Marginal MAP is a difficult mixed inference task for graphical models. Existing state-of-the-art solvers for this task are based on a hybrid best-first and depth-first search scheme that allows them to compute upper and lower bounds on the optimal solution value in an anytime fashion. These methods however are memory intensive schemes (via the best-first component) and do not have an efficient memory management mechanism. For this reason, they are often less effective in practice, especially on difficult problem instances with very large search spaces. In this paper, we introduce a new recursive best-first search based bounding scheme that operates efficiently within limited memory and computes anytime upper and lower bounds that improve over time. An empirical evaluation demonstrates the effectiveness of our proposed approach against current solvers.

JAIR Journal 2019 Journal Article

Computing Multi-Modal Journey Plans under Uncertainty

  • Adi Botea
  • Akihiro Kishimoto
  • Evdokia Nikolova
  • Stefano Braghin
  • Michele Berlingerio
  • Elizabeth Daly

Multi-modal journey planning, which allows multiple types of transport within a single trip, is becoming increasingly popular, due to a strong practical interest and an increasing availability of data. In real life, transport networks feature uncertainty. Yet, most approaches assume a deterministic environment, making plans more prone to failures such as missed connections and major delays in the arrival. This paper presents an approach to computing optimal contingent plans in multi-modal journey planning. The problem is modeled as a search in an and/or state space. We describe search enhancements used on top of the AO* algorithm. Enhancements include admissible heuristics, multiple types of pruning that preserve the completeness and the optimality, and a hybrid search approach with a deterministic and a nondeterministic search. We demonstrate an NP-hardness result, with the hardness stemming from the dynamically changing distributions of the travel time random variables. We perform a detailed empirical analysis on realistic transport networks from cities such as Montpellier, Rome and Dublin. The results demonstrate the effectiveness of our algorithmic contributions, and the benefits of contingent plans as compared to standard sequential plans, when the arrival and departure times of buses are characterized by uncertainty.

IJCAI Conference 2019 Conference Paper

Depth-First Memory-Limited AND/OR Search and Unsolvability in Cyclic Search Spaces

  • Akihiro Kishimoto
  • Adi Botea
  • Radu Marinescu

Computing cycle-free solutions in cyclic AND/OR search spaces is an important AI problem. Previous work on optimal depth-first search strongly assumes the use of consistent heuristics, the need to keep all examined states in a transposition table, and the existence of solutions. We give a new theoretical analysis under relaxed assumptions where previous results no longer hold. We then present a generic approachto proving unsolvability, and apply it to RBFAOO and BLDFS, two state-of-the-art algorithms. We demonstrate the performance in domain-independent nondeterministic planning

NeurIPS Conference 2019 Conference Paper

Depth-First Proof-Number Search with Heuristic Edge Cost and Application to Chemical Synthesis Planning

  • Akihiro Kishimoto
  • Beat Buesser
  • Bei Chen
  • Adi Botea

Search techniques, such as Monte Carlo Tree Search (MCTS) and Proof-Number Search (PNS), are effective in playing and solving games. However, the understanding of their performance in industrial applications is still limited. We investigate MCTS and Depth-First Proof-Number (DFPN) Search, a PNS variant, in the domain of Retrosynthetic Analysis (RA). We find that DFPN's strengths, that justify its success in games, have limited value in RA, and that an enhanced MCTS variant by Segler et al. significantly outperforms DFPN. We address this disadvantage of DFPN in RA with a novel approach to combine DFPN with Heuristic Edge Initialization. Our new search algorithm DFPN-E outperforms the enhanced MCTS in search time by a factor of 3 on average, with comparable success rates.

AAAI Conference 2018 Conference Paper

AI Meets Chemistry

  • Akihiro Kishimoto
  • Beat Buesser
  • Adi Botea

We argue that chemistry should be the next grand challenge for Artificial Intelligence. The AI research community and humanity would benefit tremendously from focusing AI research on chemistry on a regular basis, as a benchmark as well as a real-world application domain. To support our position, we review the importance of chemical compound discovery and synthesis planning and discuss the properties of search spaces in a chemistry problem. Knowledge acquired in domains such as two-player board games or single-player puzzles places the AI community in a good position to solve critical problems in the chemistry domain. Yet, we show that searching in chemistry problems poses significant additional challenges that will have to be addressed. Finally, we envision how several AI areas like Natural Language Processing, Machine Learning, planning and search, are relevant for chemistry.

SoCS Conference 2018 Conference Paper

On the Complexity of Quantum Circuit Compilation

  • Adi Botea
  • Akihiro Kishimoto
  • Radu Marinescu 0002

Quantum circuit compilation (QCC) is an important problem in the emerging field of quantum computing. The problem has a strong relevance to combinatorial search, as solving approaches recently published include constraint programming and temporal planning. In this paper, we focus on a complexity analysis of quantum circuit compilation. We formulate a makespan optimization problem based on QCC, and prove that the problem is NP-complete. To the best of our knowledge, this is the first study on the theoretical complexity of QCC.

IJCAI Conference 2017 Conference Paper

A Scalable Approach to Chasing Multiple Moving Targets with Multiple Agents

  • Fan Xie
  • Adi Botea
  • Akihiro Kishimoto

Chasing multiple mobile targets with multiple agents is important in several applications, such as computer games and police chasing scenarios. Existing approaches can compute optimal policies. However, they have a limited scalability, as they implement expensive minimax searches. We introduce a sub-optimal but scalable approach that assigns individual agents to individual targets and that can dynamically re-compute such assignments. We provide a theoretical analysis, including upper bounds on the number of time steps required to solve an instance. In a detailed empirical evaluation on grid maps, our algorithm scales up very convincingly beyond the limits of previous methods. On small problems, where a comparison to a minimax approach is possible, the results demonstrate a good solution quality for our method.

IJCAI Conference 2017 Conference Paper

Efficient Optimal Search under Expensive Edge Cost Computation

  • Masataro Asai
  • Akihiro Kishimoto
  • Adi Botea
  • Radu Marinescu
  • Elizabeth M. Daly
  • Spyros Kotoulas

Optimal heuristic search has been successful in many domains, including journey planning, route planning and puzzle solving. Existing work typically assumes that the cost of each action can easily be obtained. However, in many problems, the exact edge cost is expensive to compute. Existing search algorithms face a significant performance bottleneck, due to an excessive overhead associated with dynamically calculating exact edge costs. We present DEA*, an algorithm for problems with expensive edge cost computations. DEA* combines heuristic edge cost evaluations with delayed node expansions, reducing the number of exact edge computations. We formally prove that DEA* is optimal and it is efficient with respect to the number of exact edge cost computations. We empirically evaluate DEA* on multiple-worker routing problems where the exact edge cost is calculated by invoking an external multi-modal journey planning engine. The results demonstrate the effectiveness of our ideas in reducing the computational time and improving the solving ability. In addition, we show the advantages of DEA* in domain-independent planning, where we simulate that accurate edge costs are expensive to compute.

ECAI Conference 2016 Conference Paper

Combining Deterministic and Nondeterministic Search for Optimal Journey Planning Under Uncertainty

  • Akihiro Kishimoto
  • Adi Botea
  • Elizabeth M. Daly

Optimal multi-modal journey planning under uncertainty is a challenging problem, due in part to an increased branching factor generated by nondeterministic actions. Deterministic search, which ignores all uncertainty, can be much faster, but deterministic plans lack correctness and optimality guarantees in the uncertainty-aware domain.

ICAPS Conference 2016 Conference Paper

Evaluation of Auction-Based Multi-Robot Routing by Parallel Simulation

  • Akihiro Kishimoto
  • Kiyohito Nagano

Auction methods are a promising approximation approach for distributed routing including multi-robot routing, where targets on a map need to be allocated to agents while a team objective is satisfied. While many algorithms based on sequential single-item (SSI) auctions have been presented, they are currently evaluated by serial simulation where agents serially calculate their bids on a single machine. We consider a scenario where a bidding algorithm incurs significant computational overhead due to on-demand calculations of the shortest distances on a road map. We evaluate the bidding algorithm under parallel simulations where agents perform bid calculations simultaneously on a parallel machine, and reveal that the algorithm suffers from severe synchronization overhead ignored by serial simulation. We also present the broadcasting and speculation techniques to alleviate such synchronization overhead. Our empirical results on multi-robot routing variants show that both techniques improve the efficiency of parallelization, and speculation achieves more significant improvement.

ECAI Conference 2016 Conference Paper

Scalable Exact MAP Inference in Graphical Models

  • Radu Marinescu 0002
  • Akihiro Kishimoto
  • Adi Botea

This paper presents parallel dovetailing in a distributed-memory environment for exact MAP inference in graphical models. Parallel dovetailing is a simple procedure which performs multiple searches in parallel with different parameter configurations. We evaluate empirically the performance of parallel dovetailing with three state-of-the-art AND/OR search algorithms in solving various MAP inference benchmarks. Our results clearly show that parallel dovetailing is effective, yielding considerable speedups and improving the solving abilities of these state-of-the-art baseline methods.

NeurIPS Conference 2015 Conference Paper

Parallel Recursive Best-First AND/OR Search for Exact MAP Inference in Graphical Models

  • Akihiro Kishimoto
  • Radu Marinescu
  • Adi Botea

The paper presents and evaluates the power of parallel search for exact MAP inference in graphical models. We introduce a new parallel shared-memory recursive best-first AND/OR search algorithm, called SPRBFAOO, that explores the search space in a best-first manner while operating with restricted memory. Our experiments show that SPRBFAOO is often superior to the current state-of-the-art sequential AND/OR search approaches, leading to considerable speed-ups (up to 7-fold with 12 threads), especially on hard problem instances.

UAI Conference 2014 Conference Paper

Recursive Best-First AND/OR Search for Optimization in Graphical Models

  • Akihiro Kishimoto
  • Radu Marinescu 0002

The paper presents and evaluates the power of limited memory best-first search over AND/OR spaces for optimization tasks in graphical models. We propose Recursive Best-First AND/OR Search with Overestimation (RBFAOO), a new algorithm that explores the search space in a best-first manner while operating with restricted memory. We enhance RBFAOO with a simple overestimation technique aimed at minimizing the overhead associated with re-expanding internal nodes and prove correctness and completeness of RBFAOO. Our experiments show that RBFAOO is often superior to the current stateof-the-art approaches based on AND/OR search, especially on very hard problem instances.

AIJ Journal 2013 Journal Article

Evaluation of a simple, scalable, parallel best-first search strategy

  • Akihiro Kishimoto
  • Alex Fukunaga
  • Adi Botea

Large-scale, parallel clusters composed of commodity processors are increasingly available, enabling the use of vast processing capabilities and distributed RAM to solve hard search problems. We investigate Hash-Distributed A⁎ (HDA⁎), a simple approach to parallel best-first search that asynchronously distributes and schedules work among processors based on a hash function of the search state. We use this approach to parallelize the A⁎ algorithm in an optimal sequential version of the Fast Downward planner, as well as a 24-puzzle solver. The scaling behavior of HDA⁎ is evaluated experimentally on a shared memory, multicore machine with 8 cores, a cluster of commodity machines using up to 64 cores, and large-scale high-performance clusters, using up to 2400 processors. We show that this approach scales well, allowing the effective utilization of large amounts of distributed memory to optimally solve problems which require terabytes of RAM. We also compare HDA⁎ to Transposition-table Driven Scheduling (TDS), a hash-based parallelization of IDA⁎, and show that, in planning, HDA⁎ significantly outperforms TDS. A simple hybrid which combines HDA⁎ and TDS to exploit strengths of both algorithms is proposed and evaluated.

SoCS Conference 2012 Conference Paper

Diverse Depth-First Search in Satisificing Planning

  • Akihiro Kishimoto
  • Rong Zhou 0001
  • Tatsuya Imai

Diverse best-first search (DBFS) is a successful algorithm for satisficing planning that is built on top of greedy best-first search and uses stochastic search techniques to select the next ``best

SoCS Conference 2012 Conference Paper

Iterative Resource Allocation for Memory Intensive Parallel Search Algorithms (Extended Abstract)

  • Alex S. Fukunaga
  • Akihiro Kishimoto
  • Adi Botea

The increasing availability of “utility computing” resources such as clouds, grids, and massively parallel shared clusters can provide practically unlimited processing and memory capacity on demand, at some cost per unit of resource usage. This requires a new perspective in the design and evaluation of parallel search algorithms. Previous work in parallel search implicitly assumed ownership of a cluster with a static amount of CPU cores and RAM, and emphasized wallclock runtime. With utility computing resources, trade-offs between performance and monetary costs must be considered. This paper considers dynamically increasing the usage of utility computing resources until a problem is solved. Efficient resource allocation policies are analyzed in comparison with an optimal allocation strategy. We evaluate our iterative allocation strategy by applying it to the HDA* parallel search algorithm. The experimental results validate our theoretical predictions. They show that, in practice, the costs incurred by iterative allocation are reasonably close to an optimal (but a priori unknown) policy, and are significantly better than the worst-case analytical bounds.

AAAI Conference 2012 Conference Paper

Iterative Resource Allocation for Memory Intensive Parallel Search Algorithms on Clouds, Grids, and Shared Clusters

  • Alex Fukunaga
  • Akihiro Kishimoto
  • Adi Botea

The increasing availability of “utility computing” resources such as clouds, grids, and massively parallel shared clusters can provide practically unlimited processing and memory capacity on demand, at some cost per unit of resource usage. This requires a new perspective in the design and evaluation of parallel search algorithms. Previous work in parallel search implicitly assumed ownership of a cluster with a static amount of CPU cores and RAM, and emphasized wallclock runtime. With utility computing resources, trade-offs between performance and monetary costs must be considered. This paper considers dynamically increasing the usage of utility computing resources until a problem is solved. Efficient resource allocation policies are analyzed in comparison with an optimal allocation strategy. We evaluate our iterative allocation strategy by applying it to the HDA* parallel search algorithm. The experimental results validate our theoretical predictions. They show that, in practice, the costs incurred by iterative allocation are reasonably close to an optimal (but a priori unknown) policy, and are significantly better than the worst-case analytical bounds.

SoCS Conference 2011 Conference Paper

A Novel Technique for Avoiding Plateaus of Greedy Best-First Search in Satisficing Planning

  • Tatsuya Imai
  • Akihiro Kishimoto

Heuristic functions play an important role in drastically improving performance of satisficing planners based on greedy best-first search (GBFS). While automatic generation of heuristic functions (e. g. , (Hoffmann and Nebel 2001; Helmert 2006)) enables state-of-the-art satisficing planners to solve very complicated planning problems including benchmarks in the International Planning Competitions, accurate evaluations of nodes still remain as a challenging task. Although GBFS is fundamental and powerful in planning, it has an essential drawback when heuristic functions return inaccurate estimates. Assume that a heuristic function underestimates the difficulties of unpromising nodes. Then, since GBFS must expand nodes with small heuristic values first, it spends most of time in searching only unpromising areas and delays moving to the promising part. Previous work tackles this issue by adding a diversity to search, which is an ability in simultaneously exploring different parts of the search space to bypass large errors in heuristic functions. Several algorithms combined with diversity (e. g. , K-best-first search (KBFS) in (Felner, Kraus, and Korf 2003)) are empirically shown to be superior to naive best-first search algorithms. However, they still have limited diversity, since they do not immediately expand nodes mistakenly evaluated as very unpromising ones. This paper presents a new technique called diverse best-first search (DBFS), which incorporates a diversity into search in a different way than previous search-based approaches. We show empirical results clearly showing that DBFS is effective in satisficing planning.

AAAI Conference 2011 Conference Paper

A Novel Technique for Avoiding Plateaus of Greedy Best-First Search in Satisficing Planning

  • Tatsuya Imai
  • Akihiro Kishimoto

Greedy best-first search (GBFS) is a popular and effective algorithm in satisficing planning and is incorporated into high-performance planners. GBFS in planning decides its search direction with automatically generated heuristic functions. However, if the heuristic functions evaluate nodes inaccurately, GBFS may be misled into a valueless search direction, thus resulting in performance degradation. This paper presents a simple but effective algorithm considering a diversity of search directions to avoid the errors of heuristic information. Experimental results in solving a variety of planning problems show that our approach is successful.

IJCAI Conference 2011 Conference Paper

Evaluations of Hash Distributed A* in Optimal Sequence Alignment

  • Yoshikazu Kobayashi
  • Akihiro Kishimoto
  • Osamu Watanabe

Hash Distributed A* (HDA*) is a parallel A* algorithm that is proven to be effective in optimal sequential planning with unit edge costs. HDA* leverages the Zobrist function to almost uniformly distribute and schedule work among processors. This paper evaluates the performance of HDA* in optimal sequence alignment. We observe that with a large number of CPU cores HDA* suffers from an increase of search overhead caused by reexpansions of states in the closed list due to nonuniform edge costs in this domain. We therefore present a new work distribution strategy limiting processors to distribute work, thus increasing the possibility of detecting such duplicate search effort. We evaluate the performance of this approach on a cluster of multi-core machines and show that the approach scales well up to 384 CPU cores.

SoCS Conference 2011 Conference Paper

Scalable Distributed Monte-Carlo Tree Search

  • Kazuki Yoshizoe
  • Akihiro Kishimoto
  • Tomoyuki Kaneko
  • Haruhiro Yoshimoto
  • Yutaka Ishikawa

Monte-Carlo Tree Search (MCTS) is remarkably successful in two-player games, but parallelizing MCTS has been notoriously difficult to scale well, especially in distributed environments. For a distributed parallel search, transposition-table driven scheduling (TDS) is known to be efficient in several domains. We present a massively parallel MCTS algorithm, that applies the TDS parallelism to the Upper Confidence bound Applied to Trees (UCT) algorithm, which is the most representative MCTS algorithm. To drastically decrease communication overhead, we introduce a reformulation of UCT called Depth-First UCT. The parallel performance of the algorithm is evaluated on clusters using up to 1, 200 cores in artificial game-trees. We show that this approach scales well, achieving 740-fold speedups in the best case.

AAAI Conference 2010 Conference Paper

Dealing with Infinite Loops, Underestimation, and Overestimation of Depth-First Proof-Number Search

  • Akihiro Kishimoto

Depth-first proof-number search (df-pn) is powerful AND/OR tree search to solve positions in games. However, df-pn has a notorious problem of infinite loops when applied to domains with repetitions. Df-pn(r) cures it by ignoring proof and disproof numbers that may lead to infinite loops. This paper points out that df-pn(r) has a serious issue of underestimating proof and disproof numbers, while it also suffers from the overestimation problem occurring in directed acyclic graph. It then presents two practical solutions to these problems. While bypassing infinite loops, the threshold controlling algorithm (TCA) solves the underestimation problem by increasing the thresholds of df-pn. The source node detection algorithm (SNDA) detects the cause of overestimation and modifies the computation of proof and disproof numbers. Both TCA and SNDA are implemented on top of df-pn to solve tsume-shogi (checkmating problem in Japanese chess). Results show that df-pn with TCA and SNDA is far superior to df-pn(r). Our tsume-shogi solver is able to solve several difficult positions previously unsolved by any other solvers.

SoCS Conference 2010 Conference Paper

On the Scaling Behavior of HDA

  • Akihiro Kishimoto
  • Alex S. Fukunaga
  • Adi Botea

HDA* is a simple, parallelization of A* where work is asynchronously distributed among the nodes by a global hash function. Using up to 1024 cores on a large distributed memory cluster, we evaluate HDA* for a domain-independent planner as well an application-specific 24-puzzle solver. We show that HDA* scales fairly well on a large cluster using up to 1024 cores. Our analysis of the scaling behavior shows that on a cluster of multicore nodes, using only a subset of the available cores and leaving some cores idle can, surprisingly, lead to better results.

SoCS Conference 2010 Conference Paper

On Transposition Tables for Single-Agent Search and Planning: Summary of Results

  • Yuima Akagi
  • Akihiro Kishimoto
  • Alex S. Fukunaga

Transposition tables are a well-known method for pruning duplicates in heuristic search. This paper presents a detailed analysis of transposition tables for IDA*. We show that some straightforward implementations of IDA* with transposition tables (IDA*+TT) can result in suboptimal solutions being returned. Furthermore, straightforward implementations of IDA*+TT are not complete. We identify several variants of IDA*+TT which are guaranteed to return the optimal solution, as well as a complete variant. An empirical study shows that IDA*+TT can significantly improve upon the performance of A* in domain-independent planning.

SoCS Conference 2010 Conference Paper

Simultaneously Searching with Multiple Settings: An Alternative to Parameter Tuning for Suboptimal Single-Agent Search Algorithms

  • Richard Valenzano
  • Nathan R. Sturtevant
  • Jonathan Schaeffer 0001
  • Karen Buro
  • Akihiro Kishimoto

Many search algorithms have parameters that need to be tuned to get the best performance. Typically, the parameters are tuned offline, resulting in a generic setting that is supposed to be effective on all problem instances. For suboptimal single-agent search, problem-instance-specific parameter settings can result in substantially reduced search effort. We consider the use of dovetailing as a way to take advantage of this fact. Dovetailing is a procedure that performs search with multiple parameter settings simultaneously. Dovetailing is shown to improve the search speed of weighted IDA* by several orders of magnitude and to generally enhance the performance of weighted RBFS. This procedure is trivially parallelizable and is shown to be an effective form of parallelization for WA* and BULB. In particular, using WA* with parallel dovetailing yields good speedups in the sliding-tile puzzle domain, and increases the number of problems solved when used in an automated planning system.

ICAPS Conference 2010 Conference Paper

Simultaneously Searching with Multiple Settings: An Alternative to Parameter Tuning for Suboptimal Single-Agent Search Algorithms

  • Richard Valenzano
  • Nathan R. Sturtevant
  • Jonathan Schaeffer 0001
  • Karen Buro
  • Akihiro Kishimoto

Many search algorithms have parameters that need to be tuned to get the best performance. Typically, the parameters are tuned offline, resulting in a generic setting that is supposed to be effective on all problem instances. For suboptimal single-agent search, problem-instance-specific parameter settings can result in substantially reduced search effort. We consider the use of dovetailing as a way to take advantage of this fact. Dovetailing is a procedure that performs search with multiple parameter settings simultaneously. Dovetailing is shown to improve the search speed of weighted IDA* by several orders of magnitude and to generally enhance the performance of weighted RBFS. This procedure is trivially parallelizable and is shown to be an effective form of parallelization for WA* and BULB. In particular, using WA* with parallel dovetailing yields good speedups in the sliding-tile puzzle domain, and increases the number of problems solved when used in an automated planning system.

ICAPS Conference 2009 Conference Paper

Scalable, Parallel Best-First Search for Optimal Sequential Planning

  • Akihiro Kishimoto
  • Alex S. Fukunaga
  • Adi Botea

Large-scale, parallel clusters composed of commodity processors are increasingly available, enabling the use of vast processing capabilities and distributed RAM to solve hard search problems. We investigate parallel algorithms for optimal sequential planning, with an emphasis on exploiting distributed memory computing clusters. In particular, we focus on an approach which distributes and schedules work among processors based on a hash function of the search state. We use this approach to parallelize the A* algorithm in the optimal sequential version of the Fast Downward planner. The scaling behavior of the algorithm is evaluated experimentally on clusters using up to 128 processors, a significant increase compared to previous work in parallelizing planners. We show that this approach scales well, allowing us to effectively utilize the large amount of distributed memory to optimally solve problems which require hundreds of gigabytes of RAM to solve. We also show that this approach scales well for a single, shared-memory multicore machine.

AAMAS Conference 2008 Conference Paper

Optimized Algorithms for Multi-Agent Routing

  • Akihiro Kishimoto
  • Nathan Sturtevant

Auction methods have been successfully used for coordinating teams of robots in the multi-robot routing problem, a representative domain for multi-agent coordination. Solutions to this problem typically use bids computed using the shortest distance between various locations on a map. But, the cost of this shortest-distance computation has not been considered in previous research. This paper presents a new auction-based algorithm, FastBid, that works to reduce the computational costs associated with bidding in the multirobot routing problem. We also analyze how a small modification in the bidding algorithm can reduce the computational load of the bidding process. Experiments demonstrate that FastBid not only scales much better than previous approaches, but does so with little or no loss in solution quality.

IJCAI Conference 2007 Conference Paper

  • Kazuki Yoshizoe
  • Akihiro Kishimoto
  • Martin M
  • uuml; ller

Thomsen's λ search and Nagai's depth-first proof-number (DFPN) search are two powerful but very different AND/OR tree search algorithms. Lambda Depth-First Proof Number search (LDFPN) is a novel algorithm that combines ideas from both algorithms. λ search can dramatically reduce a search space by finding different levels of threat sequences. DFPN employs the notion of proof and disproof numbers to expand nodes expected to be easiest to prove or disprove. The method was shown to be effective for many games. Integrating λ order with proof and disproof numbers enables LDFPN to select moves more effectively, while preserving the efficiency of DFPN. LDFPN has been implemented for capturing problems in Go and is shown to be more efficient than DFPN and more robust than an algorithm based on classical λ search.

AAAI Conference 2005 Conference Paper

Search versus Knowledge for Solving Life and Death Problems in Go

  • Akihiro Kishimoto

In games research, Go is considered the classical board game that is most resistant to current AI techniques. Large-scale knowledge engineering has been considered indispensable for building state of the art programs, even for subproblems such as Life and Death, or tsume-Go. This paper describes the technologies behind TSUMEGO EXPLORER, a high-performance tsume-Go search engine for enclosed problems. In empirical testing, this engine outperforms GoTools, which has been the undisputedly best tsume-Go program for 15 years.

AAAI Conference 2004 Conference Paper

A General Solution to the Graph History Interaction Problem

  • Akihiro Kishimoto
  • Martin Müller

Since the state space of most games is a directed graph, many game-playing systems detect repeated positions with a transposition table. This approach can reduce search effort by a large margin. However, it suffers from the so-called Graph History Interaction (GHI) problem, which causes errors in games containing repeated positions. This paper presents a practical solution to the GHI problem that combines and extends previous techniques. Because our scheme is general, it is applicable to different game tree search algorithms and to different domains. As demonstrated with the two algorithms αβ and df-pn in the two games checkers and Go, our scheme incurs only a very small overhead, while guaranteeing the correctness of solutions.

v2026.09.13