Activities
Events Records

Jun KAWAHARA (Kyoto U., Group B01) will give a talk in the organized session "Autonomous decision making under complex conditions or situations" of the 4th Asia Pacific Conference of the Prognostics and Health Management Society (PHMAP 2023).2023.09.13 Wed. 14:0014:20Jun Kawahara, Chuta Yamaoka, Takehiro Ito, Akira Suzuki, Daisuke Iioka, Shuhei Sugimura, Seiya Goto, and Takayuki Tanabe"Algorithmic Study for Power Restoration in Electrical Distribution Networks"This talk will be based on the joint press release of our research project. The organized session will be held from 13:20 to 16:00, and 7 talks are scheduled. (PHMAP 2023 will be held on September 1114.)2023.09.13 Wed. 13:2016:00Talk in International conference "PHM Asia Pacific 2023"
Speaker : Title : Sumarry : 
As a part of the research project "Fusion of Computer Science, Engineering and Mathematics Approaches for Expanding Combinatorial Reconfiguration" (head investigator: Takehiro Ito), we are going to organize a minisymposium on Combinatorial Reconfiguration in the 10th International Congress on Industrial and Applied Mathematics (ICIAM 2023). This minisymposium aims at communicating recent research trends on combinatorial reconfiguration and discussing possible future directions.
 Colin Defant (Massachusetts Institute of Technology, USA) * invited speaker
 Irene Parada (Universitat Politècnica de Catalunya, Spain) * invited speaker
 Nicholas Williams (Lancaster University, UK) * invited speaker
 Takehiro Ito (Tohoku University, Japan)
Talk Titles and Abstracts [17:4018:05] Takehiro Ito (Tohoku University, Japan)
Title: Invitation to Combinatorial ReconfigurationAbstract: Combinatorial Reconfiguration studies reachability and related questions over combinatorial structures. A typical example asks if the solution space of a Boolean formula is connected with respect to the Boolean cube topology, formed by flipping one bit at the time. Reconfiguration problems have motivation from a variety of fields such as puzzles, statistical physics and industry, and have been studied intensively in this decade from the algorithmic viewpoints. In this talk, we will give a broad introduction of combinatorial reconfiguration, and show some recent progress on the topic. [18:0518:30] Irene Parada (Universitat Politècnica de Catalunya, Spain) * invited speaker
Title: Geometric Algorithms for Modular RoboticsAbstract: Modular selfreconfigurable robots consist of individual units that can move and connect to one another to form a larger, more complex shape. A central problem that arises is how to efficiently reconfigure these robots from one shape to another while maintaining connectivity.We will explore the computational complexity of the reconfiguration problem for the most fundamental latticebased models of modular robots. Specifically, we will examine how the reconfiguration problem differs depending on the lattice and movement capabilities of the units. We will discuss efficient algorithms for universal reconfiguration in some models, while in others the problem is PSPACEcomplete, which means that it is computationally intractable. For those cases, we identify simple conditions that allow for efficient reconfiguration.Overall, this talk will provide insights into the challenges of reconfiguring modular robots and demonstrate how geometric and graph algorithms can help us tackle this problem. [18:3018:55] Colin Defant (Massachusetts Institute of Technology, USA) * invited speaker
Title: Toric Promotion and Permutoric PromotionAbstract: We introduce toric promotion as a cyclic variant of Schutzenberger's famous promotion operator. Toric promotion acts on the labelings of a graph G; it is defined as the composition of certain toggle operators, listed in a natural cyclic order. We will show that the orbit structure of toric promotion is surprisingly nice when G is a forest. We then consider more general permutoric promotion operators, which are defined as compositions of the same toggle operators, but in permuted orders. When G is a path graph, we provide a complete description of the orbit structures of all permutoric promotion operators, showing that they satisfy the cyclic sieving phenomenon. Our proof is surprisingly involved and relies on the analysis of gliding globs, sliding stones, and colliding coins. The work on permutoric promotion is joint with Rachana Madhukara and Hugh Thomas. [18:5519:20] Nicholas Williams (Lancaster University, UK) * invited speaker
Title: Triangulations of Cyclic Polytopes Through the Lens of ReconfigurationAbstract: We discuss the reconfiguration problem given by taking the set of triangulations of a cyclic polytope as the state space, with the reconfiguration moves given by bistellar flips (the higherdimensional analogue of flipping a diagonal within a quadrilateral). The state space is connected, and we will outline how this is proven using a certain partial order on the states called the higher StasheffTamari order. We will further consider as many different other aspects of the reconfiguration as time permits, including the significance of triangulations of higherdimensional cyclic polytopes for reconfigurations of lowerdimensional cyclic polytopes, efficient combinatorial descriptions of triangulations of cyclic polytopes, and the diameter of the state space.Organizers Takehiro Ito (Tohoku University, Japan)
 Yusuke Kobayashi (Kyoto University, Japan)
 Yoshio Okamoto (The University of ElectroCommunications, Japan)
2023.08.22 Tue. 17:4019:20Minisymposium on Combinatorial Reconfiguration in ICIAM 2023
Speaker : Title : Sumarry : 
We will organize the 3rd workshop on Combinatorial Reconfiguration, affiliated with the 50th International Colloquium on Automata, Languages, and Programming (ICALP2023).
 Program and Registration
This workshop will be held as a pure facetoface event. To attend our workshop, please make a registration for ICALP workshops. Aim and Scope
Combinatorial Reconfiguration studies reachability and related questions over combinatorial structures. These types of questions arise in many areas of mathematics, computer science, and related fields. A typical example asks if the solution space of a Boolean formula is connected with respect to the Boolean cube topology, formed by flipping one bit at the time. Another example of a wellstudied application is sampling from a very large configuration space by simulating a Markov chain involving local reconfigurations. Although there is now a wealth of publications on many aspects of Combinatorial Reconfiguration, including a general framework, many questions remain open. The study of Combinatorial Reconfiguration brings together problems and techniques from a variety of fields in mathematics and computer science, such as combinatorial game theory, graph and hypergraph theory, enumeration, probability theory, random sampling via Markov Chain Monte Carlo methods, bioinformatics, complexity theory, discrete geometry, statistical physics, and many others.With the success of the workshops affiliated with ICALP 2021 and ICALP 2022, this workshop aims at strengthening relations among researchers in various fields of theoretical computer science and mathematics, and broadening interest in Combinatorial Reconfiguration to a wider audience. Two invited talks by leading experts are planned as a way to build bridges to closelyrelated fields. We also plan to report the results of the 2nd Combinatorial Reconfiguration Challenge (CoRe Challenge 2023) during the workshop.
https://corechallenge.github.io/2023/
The workshop is planned to be held in person in Paderborn.The workshop is held in cooperation with JSPS KAKENHI project "Fusion of Computer Science, Engineering and Mathematics Approaches for Expanding Combinatorial Reconfiguration."
https://core.dais.is.tohoku.ac.jp/en/ Invited Speakers
 Marthe Bonamy (Université de Bordeaux, France)
 Jun Kawahara (Kyoto University, Japan) Call for Contributed Talks and Submission Guideline
Authors are invited to submit original work that is related to any aspect or application of Combinatorial Reconfiguration. Any work already or not yet published is welcome. Presentations of ongoing work and open problems, as well as challenges, are encouraged. Short survey talks are also welcome.
The submission must be formatted in one page that contains the title of the work, the list of all authors, an email address of the corresponding author, and a brief summary of the presentation. The manuscript must be prepared with the following template as a PDF file.
http://www.dais.is.tohoku.ac.jp/core2023template.zip
Even though there will be no strict formal refereeing process, some contributions might not be accepted at the discretion of the Program Committee. A collection of onepage abstracts will be distributed to the workshop participants only. Submission should be done via EasyChair.
https://easychair.org/conferences/?conf=core2023 Important Dates
 Submission deadline:April 22, 23:59 AoE(extended to) May 7, 23:59 AoE
 Notification:May 8(extended to) May 12( Early registration deadline for ICALP 2023: May 15, 23:59 CET)
 Cameraready version due: June 19, 23:59 AoE
 Date of workshop: July 10, 2023 Program Committee
 Nicolas Bousquet, CNRS, Université Lyon 1, France
 Takehiro Ito, Tohoku University, Japan (Chair)
 Naomi Nishimura, University of Waterloo, Canada
 Yoshio Okamoto, The University of ElectroCommunications, Japan
 Akira Suzuki, Tohoku University, Japan Organizing Committee
 Takehiro Ito, Tohoku University, Japan (Chair)
 Yoshio Okamoto, The University of ElectroCommunications, Japan
 Akira Suzuki, Tohoku University, Japan2023.07.10 Mon.3rd Workshop on Combinatorial Reconfiguration, affiliated with ICALP 2023
Speaker : Title : Sumarry : 
There are many realworld problems that can be formulated as combinatorial optimization problems. They tend to be NPhard and are hard to solve exactly when the instance sizes are large. As a practical way to solve such problems, heuristic algorithms are often used to find good solutions, though not necessarily optimal, in a reasonable amount of time. Standard basic heuristic strategies include greedy methods and local search algorithms. Such basic strategies are often combined to make more sophisticated methods, called metaheuristics, to find better solutions using more computation time. This talk introduces some of our results on efficient heuristic algorithms based on such strategies.2023.02.06 Mon. 10:0012:0035th CoRe Seminar
Speaker :YAGIURA, Mutsunori (Nagoya U., invited talk) Title :Practical algorithms for combinatorial optimization problems Sumarry : 
An amidakuji (i.e., ladder lotteries, or Ghost Legs) consists of n vertical lines (lines for short) and some horizontal bars (bars for short), where lines have their labels, and each bar connects two lines. By regarding each bar as the exchange of the labels of a pair of lines, an amidakuji (i.e., the network of the lines and bars) represents a permutation. Amidakuji's also correspond to sorting networks, in which bars are regarded as comparators. An amidakuji corresponds to a primitive sorting network if every bar connects two consecutive lines. A rhombus tiling is a tiling of rhombuses of unit edge length without gap or overlap. In this talk, we begin with the relation between Amidakujis and rhombus tilings. Then, we move to the enumeration by the reverse search and ZDDs (ZeroSuppressed Binary Decision Diagrams).2023.01.16 Mon. 10:0012:0034th CoRe Seminar
Speaker :HORIYAMA, Takashi (Hokkaido U., invited talk) Title :Enumeration of amidakujis and rhombus tilings Sumarry : 
As a part of the research project "Fusion of Computer Science, Engineering and Mathematics Approaches for Expanding Combinatorial Reconfiguration" (head investigator: Takehiro Ito), we are going to organize Workshop "Combinatorial Reconfiguration and FixedParameter Tractability" via Zoom on December 12, 2022 (based on European Timezone).
The objective is to learn recent developments of fixedparameter (in)tractability and their relations with combinatorial reconfiguration. In her influential survey paper "Introduction to Combinatorial Reconfiguration" (Algorithms 2018), Naomi Nishimura dedicated one section to applications of the parameterized complexity methodology to problems on combinatorial reconfiguration. Indeed, several papers have been presented along this line of research. Furthermore, the research activity on fixedparameter (in)tractability has been quite active, and there are a lot of recently introduced methods that are waiting for being applied to combinatorial reconfiguration. In this workshop, we will learn recent research trends of fixedparameter tractability and combinatorial reconfiguration, and will discuss a new connection between these two fields of theoretical computer science.This workshop aims at the broad audience of discrete mathematics and theoretical computer science, who wish to learn and work on these active research areas.The program will be exclusively composed of invited talks. Each talk is planned to span one hour, including discussion.List of Confirmed Invited Speakers Hans L. Bodlaender (Utrecht University, the Netherlands)
 Bart M. P. Jansen (Eindhoven University of Technology, the Netherlands)
 Eun Jung Kim (ParisDauphine University, France)
 Moritz Mühlenthaler (Université Grenoble Alpes, France)
 Saket Saurabh (The Institute of Mathematical Sciences, India)
RegistrationRegistration is free of charge, but please make your registration in advance.Program2022.12.12 Mon. CET (JST)08:5509:00 (16:5517:00) Welcome address 09:0010:00 (17:0018:00) Eun Jung Kim (ParisDauphine University, France)TwinWidth and Its Implications10:1511:15 (18:1519:15) Moritz Mühlenthaler (Université Grenoble Alpes, France)Constraint Satisfaction Reconfiguration11:1513:00 (19:1521:00) Lunch/Dinner Break 13:0014:00 (21:0022:00) Saket Saurabh (The Institute of Mathematical Sciences, India)FPT Approximation Schemes for the Maximum Coverage and MAXSAT Problem14:1515:15 (22:1523:15) Bart M. P. Jansen (Eindhoven University of Technology, the Netherlands)Search Space Reduction Beyond Kernelization15:3016:30 (23:3024:30) Hans L. Bodlaender (Utrecht University, the Netherlands)Parameterized Complexity of Reconfiguration of Small Independent Sets and Dominating SetsTalk Titles and Abstracts 09:0010:00 (17:0018:00)
Eun Jung Kim (ParisDauphine University, France)Title: TwinWidth and Its ImplicationsAbstract: First Order Logic (FO logic) expresses many classic computational problems such as kIndependent Set problem with variables and logical connectives. First Order model checking is known to be fixedparameter tractable on important classes such as nowhere dense classes, bounded rankwidth graphs, unit interval graphs as well as strict hereditary classes of permutations. A notion called twinwidth, introduced by Bonnet, Kim, Thomassé, Watrigant (FOCS 2020), elegantly captures vast swathes of such classes, and provides a new perspective to explain why so many computational problems are fixedparameter tractable on graph classes seemlying so different. We will briefly sketch the new notion, and its rapidly developing impact in theoretical computer science with an emphasis on algorithm designs. 10:1511:15 (18:1519:15)
Moritz Mühlenthaler (Université Grenoble Alpes, France)Title: Constraint Satisfaction ReconfigurationAbstract: The constraint satisfaction problem (CSP) asks for an assignment of values to variables such that given constraints are satisfied. Special cases of the CSP are for example graph coloring and Boolean satisfiability. We consider the following reconfiguration variant of the CSP: given two feasible solutions of a CSP instance, can we transform one solution into the other by changing the value of a single variable at a time, such that in each step the constraints are satisfied? We give an overview of what is known about the complexity of this question and highlight the techniques behind recent algorithmic results. 13:0014:00 (21:0022:00)
Saket Saurabh (The Institute of Mathematical Sciences, India)Title: FPT Approximation Schemes for the Maximum Coverage and MAXSAT ProblemAbstract: Vertex Cover is a classical NPhard problem. Partial Vertex Cover is a variant of the Vertex Cover problem where the goal is to maximize the number of edges covered, given a fixed number of vertices that can be used. Partial Vertex Cover is a W[1]hard problem. There are FPT approximation schemes for Partial Vertex Cover parameterized by the solution size, i.e., there are $(1\epsilon)$factor approximation algorithms running in time $f(k,\epsilon) n^{O(1)}$ for all $0<\epsilon<1$. In this talk, we consider the Partial Vertex Cover problem and SAT problems in hypergraphs where there is no bound on the size of the hyperedges. We design an FPT approximation scheme for these problems on hypergraphs that satisfies the Kijfree property, i.e., no $i$ vertices are contained in $j$ common hyperedges. 14:1515:15 (22:1523:15)
Bart M. P. Jansen (Eindhoven University of Technology, the Netherlands)Title: Search Space Reduction Beyond KernelizationAbstract: The framework of kernelization gives a mathematical model for the rigorous analysis of preprocessing, aimed at showing that any instance with parameter k can efficiently be reduced to an equivalent one whose size depends only on k. Kernelization serves as a useful tool to obtain FPT algorithms, since any bruteforce algorithm solves the reduced instance in time depending only on k. However, from the definition of kernelization it is not clear why kernelization would lead to significant speedups when the reduced instance is not solved by brute force, but by a fixedparameter tractable algorithm whose running time is governed by the value of the parameter. To speed up such algorithms, it is the parameter controlling the size of the search space which should decrease, rather than the encoding size of the input. The discrepancy between reducing the instance size versus decreasing the search space is the focus of this talk. The quest for preprocessing algorithms that reduce the search space leads to a new type of algorithmic and graphtheoretical questions. The talk gives an introduction to this budding line of inquiry by presenting examples from recent work on the search for essential vertices and antler structures in graphs.
Based on joint work with Benjamin M. Bumpus, Huib Donkers, and Jari J.H. de Kroon. 15:3016:30 (23:3024:30)
Hans L. Bodlaender (Utrecht University, the Netherlands)Title: Parameterized Complexity of Reconfiguration of Small Independent Sets and Dominating SetsAbstract: In this talk, we look at the complexity of reconfiguring independent or dominating sets, where we assume that the size of the sets is a small parameter k, under different rules of moving the "tokens". It appears that the parameterized complexity depends on the assumption of how the number of moves that can be made is specified, but less on the type of moves.
Some related literature is also reviewed.Organizers Takehiro Ito (Tohoku University, Japan)
 Yoshio Okamoto (The University of ElectroCommunications, Japan)
 Yota Otachi (Nagoya University, Japan)
2022.12.12 Mon.Workshop "Combinatorial Reconfiguration and FixedParameter Tractability"
Speaker : Title : Sumarry : 
I will introduce the theoretical field of distributed computing to you in this talk by explaining recent results on two problems in the field. Specifically, I will talk about
(i) the leader election problem in the population protocol model, and
(ii) Byzantine gathering problem by mobile agents.The population protocol model represents a network consisting of tiny sensors that moves passibly (i.e., they constantly move, but cannot control their own move). This model was proposed by Angluin et al. in 2004 and has been intensively studied since then. In particular, the leader election problem and the majority problem are well studied. In this talk, I will discuss the former, that is, the leader election problem.Mobile agents are mobile entity that moves autonomously on a computer network. The gathering problem is a wellstudied fundamental problem, which requires all agents to gather at a single node. In this talk, we will discuss a variant of this problem, i.e., the gathering problem with the assumption that some agents take arbitrary adversarial actions.2022.12.05 Mon. 10:0012:0033rd CoRe Seminar
Speaker :SUDO, Yuichi (Hosei U., invited talk) Title :The theoretical field of distributed computing Sumarry : 
I am a researcher in the field of electric power and energy. I am researching mechanisms to maximize the introduction of renewable energy sources on the premise of ensuring safety, stable supply, economic efficiency, and environmental conservation. One of the issues in increasing the introduction of renewable energy sources is the degradation of power quality, which adversely affects social life. In this presentation, the mechanism and countermeasures for power quality degradation caused by renewable energy source will be described, and research to expand the amount of renewable energy sources that can be introduced will be introduced.2022.11.28 Mon. 10:0012:0032nd CoRe Seminar
Speaker :IIOKA, Daisuke (Chubu U., Group B01) Title :Development of electric power system based mainly on renewable energy sources Sumarry : 
Dynamical Systems is a field that studies the collective behavior of objects that update their states according to some rules. DiscreteTime Boolean Finite Dynamical System (DTBFDS) is a subfield where the systems have some finite number of objects whose states are Boolean values, and the state updates occur in discrete time. In the subfield of DTBFDS, researchers aim to (i) design models for capturing realworld phenomena and using the models to make predictions and (ii) develop simulation techniques for acquiring insights about the systems' behavior. Useful for both aims is understanding the system dynamics mathematically before executing the systems. Obtaining a mathematical understanding of BFDS is quite challenging, even for simple systems, because the state space of a system grows exponentially in the number of objects. Researchers have used computational complexity to circumvent the challenge. The complexity theoretic research in DTBFDS has successfully produced complete characterizations for many dynamical problems.The DTBFDS studies have mainly dealt with deterministic models, where the update at each time step is deterministic, so the system dynamics are completely determinable from the initial setting. However, natural systems have uncertainty. Models having uncertainty may lead to farbetter understandings of nature. Although a few attempts have explored DTBFDS with uncertainty, including stochastic initialization and tiebreaking, they have scratched only a tiny surface of models with uncertainty. The introduction of uncertainty can be through two schemes. One is the introduction of alternate update functions. The other is the introduction of alternate update schedules. In this talk, I present a set of new DTBFDS models with uncertainty and present some initial results.
2022.11.14 Mon. 10:0012:0031st CoRe Seminar
Speaker :OGIHARA, Mitsunori (U. Miami, invited talk) Title :A theory for discretetime Boolean finite dynamical systems with uncertainty Sumarry : 
In the krecoloring problem, we are given two (vertex)colorings of a graph using k colors, and asked to transform one into the other by recoloring only one vertex at a time, while at all times maintaining a proper kcoloring. In this talk, we consider a (directed) recolorability constraint on the k colors, which forbids some pairs of colors to be recolored directly. The recolorability constraint is given in terms of a digraph, whose vertices correspond to the colors and whose arcs represent the pairs of colors that can be recolored directly. We provide algorithms for the problem based on the structure of the digraph, showing that the problem is solvable in linear time when the digraph is a directed cycle or is in a class of multitrees. This talk is based on joint work with Soichiro Fujii, Yuni Iwamasa, and Akira Suzuki.2022.10.31 Mon. 10:0012:0030th CoRe Seminar
Speaker :KIMURA, Kei (Kyushu U., invited talk) Title :Algorithms for coloring reconfiguration under recolorability digraphs Sumarry :