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Queen’s Discrete-Event Systems Lab

At Queen's University in Kingston, Ontario
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Contact Us:    613-533-2966 (Prof. Rudie)

We work on the control of discrete-event systems (DES). We are interested in processes whose behaviour is described by sequences of events or actions and which require some form of control to induce desirable behaviour. Work in this area focuses on mathematically modeling such systems and on searching for solutions to control problems. Some of the areas of application are emergency response protocols, computer systems, manufacturing plants, telecommunication networks and robotics. The mathematical tools used include formal languages and automata theory, mathematical logic, graph theory and algebra.

Some of our interests and recent joint projects include the following:

  • formal mathematical models and software tools for emergency response to large-scale disasters or crises such as health epidemics or water contamination
  • control and communication protocols for decentralized discrete-event problems where agents with only partial observations (due to limited sensor access) communicate in order to gain information
  • a modal logic for "knowledge" to model discrete-event control problems
  • mathematical models of telecommunication problems so that discrete-event control theory can aid in protocol verification or can lead to protocol synthesis
  • the use of cognitive science to understand the way people solve discrete-event systems problems so that this can be used to improve discrete-event system software
  • an application of discrete-event control theory to determine where concurrency control should be inserted into software programs
  • the use of graph theory to explore how and when the computational complexity of some DES operations that arise under partial observation can be characterized or decreased

In general, we are interested in connecting discrete-event systems theory with other distributed-system problems that may arise in computer systems, in economic systems, and in telecommunication systems.

Our research is funded, in great part, by the Natural Sciences and Engineering Research Council (NSERC).

Current Members

Supervisor

Karen Rudie
Karen Rudie    karen.rudie(a)queensu.ca
(613) 533-2966/2925    http://www.ece.queensu.ca/People/K-Rudie/
  • Professor, Department of Electrical and Computer Engineering, Queen's University; cross-appointed to the School of Computing, Queen's
  • Received Ph.D. in 1992 from the University of Toronto in the Systems Control Group, Department of Electrical Engineering, under the supervision of Prof. W.M. Wonham
  • Associate Editor for IEEE Transactions on Control Systems Technology (since 2015) and Department Editor for Journal of Discrete Event Dynamic Systems: Theory and Applications (since 2019)
  • Served on the IEEE Board of Governors (2001-2003) and as Associate Editor for Journal of Discrete Event Dynamic Systems: Theory and Applications (2000-2018), IEEE Transactions on Automatic Control (1996-1999) and IEEE Control Systems Magazine (2003)
  • Teaching recognition and awards include two Golden Apple Awards (1998, 2002) from the Faculty of Applied Science, thirteen awards from the Department of Electrical and Computer Engineering (2019, two in 2018, two in 2017, two in 2016, 2015, 2014, 2013, 2012, 2001, 1998) and inclusion for five years in the Maclean's Guide to Canadian Universities in their list of "Popular Profs" at Queen's University (2003-2007)
  • IEEE Control Systems Society Distinguished Lecturer (2004-2006)
  • IEEE Fellow (since 2018)

Graduate Students

Michel Rodrigo's photo
Michel Rodrigo das Chagas Alves michelrodrigo(a)ufmg.br
  • Ph.D. student in the Graduate Program in Electrical Engineering at Universidade Federal de Minas Gerais, Brazil. Co-supervised by Dr. Patricia Pena (UFMG).
  • Received M.Eng. from the Graduate Program in Electrical Engineering at Universidade Federal de Minas Gerais, Brazil (2018).
  • Received B.Eng. in Control and Automation Engineering from the Universidade Federal de Minas Gerais, Brazil (2016).
  • Received technician degree in Electrotechnics from the Centro Federal de Educação Tecnológica de Minas Gerais, Brazil (2009).
  • Work Experience:  Teacher at Centro Federal de Educação Tecnológica de Minas Gerais.
  • Research interests: Application of Control Supervisory Theory in Cyber-Security problems. Application of abstractions and the Control Supervisory Theory in Planning problems.
Jeremy Kulchyk jeremy.kulchyk(a)queensu.ca
  • M.A.Sc. candidate in the Department of Electrical and Computer Engineering at Queen's University
  • Received B.A.Sc. in Applied Mathematics with a focus on Systems and Robotics from Queen's University (Sci'18)
  • Work Experience: Full stack developer at Two Rings Media (2016-2018)
  • Research Interests: Opacity of discrete event systems applied to fleets of mobile agents
Richard Hugh Moulton 17rhm(a)queensu.ca
   Richard Moulton's Webpage
  • Ph.D. student in the Department of Electrical and Computer Engineering at Queen's University.
  • Co-supervised by Dr. Stephen Scott in the Department of Biomedical and Molecular Science.
  • Completed MCS at the University of Ottawa in 2018.
  • Received B.Sc. Honours Computer Science from the Royal Military College of Canada in 2010.
  • Honours: FEAS Dean's Graduate Research Assistant Award (2018); Ontario Graduate Scholarhip (2017-18); NSERC Canada Graduate Scholarship - Master's (2016-17).
  • Work Experience: Aerospace Control Officer in the Canadian Armed Forces (2006-16).
  • Research interests: Online learning and control of discrete event systems and applications to problems in neuroscience.
Bryony Schonewille's photo
Bryony Schonewille    14bhs1(a)queensu.ca
  • M.A.Sc. candidate in the Department of Electrical and Computer Engineering at Queen's University
  • Received B.A.Sc. from the Department of Applied Mathematics, specializing in Computers and Communications at Queen’s University (Sci’19)
  • Work Experience: Course development for APSC 200 for the Department of Mathematics and Engineering, developing a communication and localization system for a group of robots
  • Research Interests: Opacity of Discrete Event Systems as it applies to a group of autonomous, intelligent agents who can communicate locally
Richard Yan's photo
Yunshan (Richard) Yan yan.yunshan(a)queensu.ca
Richard Yan's Webpage (Chinese)
  • Ph.D. student in the Department of Electrical and Computer Engineering at Queen's University.
  • Received M.Eng. from the Department of Electrical and Computer Engineering, Queen's University (2019).
  • Received B.A.Sc. from the Department of Electrical and Computer Engineering, Queen's University (2018).
  • Work Experience: Teaching Assistance for 7 courses in my department; contracted with Easy Education (formerly A Plus Education) to provide tutoring services.
  • Research interests: Distributed opacity of discrete event systems with agents reasoning about knowledge.


Past Members

Graduate Students and Postdoctoral Researchers

Zahra Abedi Khouzani    17zak1(a)queensu.ca
  • M.A.Sc. student in the Department of Electrical and Computer Engineering at Queen's University (2017-2019)
  • Received B.Sc. in Electrical Engineering from Isfahan University of Technology (2017)
  • Research Interests: Opacity of Discrete Event Systems
Francis Atampore    atampore(a)cs.queensu.ca
  • Completed Ph.D. in the School of Computing at Queen's University, Canada, 2017. Co-supervised by Dr. Juergen Dingel and Dr. Karen Rudie.
  • Received M.Sc. in Computer Science from Brock University, Canada (August, 2012).
  • Received bachelor's degree in Computer Science and Mathematics from University of Ghana (June, 2009).
  • Research interest: Service-oriented computing, automated service and API composition, supervisory control of DES, software synthesis, formal methods and real-time systems.
Anthony Auer    ay ay you ee are(a)cs.queensu.ca
  • Vice President, Debt Products, BMO Capital Markets, 2010 - Present.
  • Completed M.Sc. in the School of Computing at Queen's University in May, 2010.
  • Received Bachelor of Science in Engineering (Engineering Physics) from Queen's University in 2001.
  • Was Co-Founder and CTO of MediaShell Corporation, 2000-2001.
  • Worked as a Senior Consultant at CGI Group Inc., 2002-2007.
Behnam Behinaein    9hbb(a)queensu.ca
  • Postdoctoral Fellow, Queen's University in Electrical and Computer Engineering (2017-18).
  • Received Ph.D. from Queen's University in Electrical and Computer Engineering (2016).
  • Received M.Sc. from Isfahan University of Technology in Electrical Engineering.
  • Received B.Sc. from Iran University of Science and Technology in Electrical Engineering
  • Research interests: Opacity of Discrete-Event Systems, systems biology, complex systems, application of graph and network theory in biology, dynamical modeling of biological systems, application of Petri nets in biology.
Stephane Blouin    stephane.blouin (a) drdc-rddc.gc.ca
(902) 426-3100 x216     
  • Received Ph.D. from Queen's University, Department of Chemical Engineering, 2003
  • Thesis Title: Finite-state Machine Abstractions of Continuous Systems.
  • Received M.Sc. from Ecole Polytechnique, Department of Electrical Engineering, 1998
  • Received B.Sc. from Laval University, Department of Mechanical Engineering, 1992
  • Current Status: Defence Scientist in Underwater Surveillance and Communications at DRDC, Atlantic Research Centre.
  • Adjunct Faculty (Process Engineering and Applied Science) at Dalhousie University.
Md Tawhid Bin Waez    waez(a)cs.queensu.ca
  • Tawhid, a Research Engineer in Ford Motor Company, USA, leads formal methods related global research activities of Ford R&AE. He has been leading a project of 34 researchers and engineers of Ford to ensure automotive functional safety standard ISO-26262 compliant product development at the software-level.
  • He eceived his PhD in Computer Science from Queen's University, Canada in 2015 under the supervision of Prof. Karen Rudie, Dept. of Electrical and Computer Engineering and Prof. Juergen Dingel, Queen's School of Computing. A Model for Hierarchical Open Real-Time Systems was the title of his PhD Thesis.
  • He received his M.Sc. in Computer Science from Bishop's University, Canada in 2009 under the supervision of Prof. Stefan Bruda.
  • He received his B.Sc. in Computer Science from North South University, Bangladesh in 2005.
  • His research interests include formal methods, functional safety standards, DES control theory, game theory, formal languages, and requirement engineering.
Christopher Dragert    christopher.dragert(a)ubisoft.com
  • Received M.Sc. in Computer Science from Queen's University, Sept. 2008.
  • Thesis Title: Generation of Concurrency Controls using Discrete-Event Systems.
  • Current Status: Ph.D. candidate in the School of Computing at McGill University in Montréal, Canada, researching software development of AI in digital computers, AI Developer for Ubisoft, located in Toronto, Canada.
Lenko Grigorov    lenko.grigorov(a)banica.org
      http://banica.org/research/
  • Received Ph.D. in Computer Science from Queen's University in 2009.
  • Received MSc. in Computer Science from Queen's University in 2004 and BSc. in Computer Science from Masaryk University, Czech Rep. in 2001.
  • Research interests include: control of time-varying discrete-event systems, knowledge extraction from discrete-event systems, information representation for humans, human-computer interaction, and others.
  • Work experience: Instructor, Software Developer, Web Designer and Developer, Computer Technician, Layout Editor, and others.
Michael Holtstrom (Formerly Michael Wood)    mholtstrom(a)fibics.com
     http://holtstrom.com/michael/
  • Current Status: Applications Developer at Fibics in Ottawa, Ontario.
  • M.Sc.Eng., Queen's University, Electrical and Computer Engineering, 2005
  • Thesis Title: Application, Implementation and Integration of Discrete-Event Systems Control Theory.
  • B.Sc.Eng., Queen's University, Electrical and Computer Engineering, 2003.
Tun Hu    tunhu(a)site.uottawa.ca
(613) 721-8688   
  • Thesis Title: Communication States in Decentralized Discrete-Event Systems.
  • Received M.Sc. from Queen's University, Department of Electrical and Computer Engineering, May 2002.
  • Current Status: Ph.D. candidate in School of Information Technology and Engineering in University of Ottawa.
Ying Huang    ying(a)ee.queensu.ca
  • Received M.Sc. (Eng.) from Queen's University, Department of Electrical and Computer Engineering, 2005.
  • Received B.Eng. in Electrical Engineering from Jinan University, P.R.China, in July, 1994.
 
Gino Labinaz     
  • Member of DES lab, 1995-2000.
  • Received Ph.D. from Queen's University, 2004.
  • Thesis title: Viability of Hybrid Systems.
 
Ekaterina Lemch     
  • Postdoctoral researcher in DES lab, 2001-2002.
  • Project Title: Intelligent Optimization of Industrial Operations (IO2).
  • Co-supervised by Prof. Martin Guay (Chemical Engineering).
  • Funded by Precarn Associates, Inc Joint Project with Hatch Associates Ltd., National Research Council, Syncrude Canada, University of British Columbia, University of Alberta, and Wenco International Mining Systems.
Shaowu Luo    sluo(a)nortel.com
(613) 967-5000 (ext. 3418)     
  • Thesis Title: A Systematic Method to Analyze Cryptographic Protocols using Discrete-Event Systems.
  • Received M.Sc. from Queen's University, Department of Electrical and Computer Engineering, September 1999
  • Current Status: Employed by Nortel Networks.
 
Arezou Mohammadi    arezoum(a)cs.queensu.ca
  • Thesis Title: Sequences that Lead to Failure in Decentralized Supervisory Control.
  • Received M.Sc. from Queen's University, Department of Electrical and Computer Engineering, 2003.
 
Adrian Payne     
  • Thesis Title: Matrix-Based Algorithms and an Analysis of System Structure for Partially-Observable Discrete-Event Systems.
  • Received M.Sc. from Queen's University, Department of Electrical and Computer Engineering, 1997.
Usman Raza    usman.raza(a)queensu.ca
  • Was candidate for M.Sc in Electrical and Computer Engineering (Biomedical Engineering specialization), Queen's University, Canada.
  • Received Bachelor's degree in Electronics and Computer Engineering from Queen's University in 2013.
  • Research interests: Machine learning, data mining, predictive analysis.
  • Current Position: Platform Engineer, Stitch Fix, San Francisco
 
Laurie Ricker    lricker(a)mta.ca
     http://www.mta.ca/~lricker
  • Received Ph.D. from Queen's University, Department of Computing and Information Science, 1999.
  • Thesis Title: Knowledge and communication in decentralized discrete-event control.
Iakov Romanovski    yasha(a)chee.queensu.ca
(613) 533-2718   
  • Postdoctoral researcher in DES lab, 2003.
  • Project Title: Hybrid Modeling for Real-Time Control of Flexible Manufacturing Systems.
  • Co-supervised by Prof. Martin Guay and Prof. Jim McLellan (Chemical Engineering).
  • Funded by Centre for Automotive Materials and Manufacturing and General Motors.
David Sears    sears(a)cs.queensu.ca
  • Received Ph.D. in the School of Computing at Queen's University, 2018.
  • Received M.Sc. from the School of Computing at Queen's University in June, 2011.
  • Received Bachelor of Computing (Software Design) from the School of Computing at Queen's University in June, 2008.
  • Honours: Recipient of the Distinguished Masters Thesis Award from the School of Computing in April, 2011.
  • Work Experience: Held teaching assistant positions in 2008, 2010 - 2012 and 2014 at the School of Computing. Held full-time positions in Software Quality Assurance at Alcatel-Lucent from 2008 - 2009 and BlackBerry Limited from 2006 - 2007.
  • Research interests: Supervisory control of DES, fault diagnosis of DES, formal languages and automata theory.
  • Current Position: Sofware Engineer, Rogue Wave
Swapan Sikdar    0ss38(a)cs.queensu.ca
  • Swapan explores allocations designs in centralized and decentralized settings. One of his current investigations concerns design of allocation queues in which participating agents self-select the queue to join. Another of his investigation considers using a multi-attribute utility function in allocation design.
  • Received Ph.D. in Electrical and Computer Engineering from Queen's University, Canada in 2016.
  • Received MASc. in Electrical and Computer Engineering from Ryerson University, Canada in 2009.
  • Received Bachelor's degree in Electronics and Communication Engineering from Indian Institute of Technology, Roorkee (previously known as University of Roorkee), India in 1978.
  • Research interests include Systems Modeling, Requirements Modeling and Adaptive Systems.
  • Shown here with his son, Sailesh, on a July night by Lake Simcoe hoping to catch a glimpse of Northern Lights.
Victoria Tolls    victoria.tolls(a)queensu.ca
  • Completed her MSc at Queen's University School of Computing (Co-supervised by Dr. David Maslove, Dr. Karen Rudie, Dr. Evelyn Morin) in 2018.
  • Recipient of the ACM SIGHPC/Intel Computational & Data Science Fellowship (2016 & 2017).
  • Received Honours BSc in Bioinformatics with distinction from Carleton University in 2016.
  • Research Interests: data visualization, biomedical informatics, bioinformatics, time-series analysis, machine learning, complex & big data
Creag Winacott    creag(a)cs.queensu.ca
  • Completed M.Sc. in the Department of Computer Science at Queen's University, 2011.
  • Received Bachelor of Computer Science (Cognitive Science) from Queen's University in June, 2007.
 
Sarah-Jane Whittaker    sarah(a)cs.queensu.ca
  • Co-founded GoSaBe Development and Design, a software and web development firm based in Kingston, Ontario, in 2011.
  • Received her Ph.D. from the department of Computer Science at Queen's University in 2011; she was co-supervised by James McLellan in the Department of Chemical Engineering and her thesis was titled "Augmenting Petri Nets to Model Health-Care Protocols".
  • Received her M.Sc. from the department of Computer Science at Queen's University in 2005.
  • Received her Bachelor of Computer Science (Software) and Minor in Mathematics from Carleton University in 2003.
  • Held co-op positions at Rational Software Corp., Entrust Technologies Ltd. and New Paradigm Technologies Inc.

Visting Scholar

Fei Wang's photo
Wang Fei    feiw545(a)163.com
  • Research visitor to QDES lab in 2018-19.
  • Associate Professor in College of Information Science and Engineering at Huaqiao University.
  • Received Ph.D. from Xian jiaotong University in Control Science and Engineering (2009)
  • Received M.Sc. from Xidian University in Management Science and Engineering.
  • Received B.Sc. from Zhengzhou University in Mathematics.
  • Research interests: Supervisory Control of Discrete-Event Systems.

Visiting Student Researchers

David Allen    david.allen(a)qimonda.com
(919) 677-6353     
  • Member of QDES lab during the summers of 1994 and 1995.
  • Summer projects included application development and conversion.
  • Received B.Sc. from Queen's University, Department of Electrical and Computer Engineering, 1996.
  • Current Status: Employed as a Senior Engineer with Qimonda.
Philippe Nguyen    nguyen_philippe(a)hotmail.com
(514) 744-9521     
  • Member of QDES lab during the summer of 2003.
  • Title of project: API and GUI for Software of Discrete-Event Systems.
  • Received B.Sc. from Queen's University, Department of Electrical and Computer Engineering (Software Option), 2004.
  • Held an Undergraduate Student Research Award (USRA) from the Natural Sciences and Engineering Research Council (NSERC).
  • Current Status: M.Sc. in Computer Science at McGill University (starting Sept. 2004).
 
Kari Pihkala     
  • Member of QDES lab during the summer of 1997.
  • Title of project: Software for Control of Discrete-Event Systems.
  • IAESTE Trainee
Kristian Edlund    ksed02(a)control.aau.dk
  • QDES lab member from Sept. 2005 - Dec. 2005.
  • Visited as part of Master's program at Aalborg University in Denmark.
  • Project title: Modelling and Implementation of Supervisory Control of Discrete-Event Systems.
  • Current Status: Industrial PhD at DONG Energy
  • Makes great beef stew.
Axel G. Michelsen    http://de-klubben.aau.dk
  • QDES lab member from Sept. 2005 - Dec. 2005.
  • Visited as part of Master's program at Aalborg University in Denmark.
  • Project title: Modelling and Implementation of Supervisory Control of Discrete-Event Systems.
  • Owns at least four awesome t-shirts.
Thomas Brunsch    brunsch(a)control.tu-berlin.de
  • Member of QDES lab during the spring and summer of 2007.
  • Visited as part of German Engineering progamm at Otto-von-Guericke University, Magdeburg, Germany.
  • Project title: Discrete-Event Systems Model of an Outbreak Response
  • Received Dipl.-Ing. from Otto-von-Guericke University, Magdeburg, Germany, 2008.
  • Received dual Ph.D. from Technical University Berlin, Germany, and University of Angers, France, 2014.
  • Current Status: Employed as an Engineer at inpro, Berlin, Germany.
Christian Silvano    christian.silvano(a)gmail.com
  • Member of QDES lab during the summer and fall of 2007.
  • IAESTE Trainee.
Valerie Sugarman
  • Member of QDES lab during the summer of 2010.
  • Continued development of IDES.
  • Held an Undergraduate Student Research Award (URSA) from the Natural Sciences and Engineering Research Council (NSERC).
  • Current Status: M.Sc student, Human Computer Interaction at the University of Waterloo (Sept. 2015).
 
Utsav Mital
  • Member of QDES lab during the summer of 2010.

Published Journal, Magazine and Conference Articles and Conference Posters

  • F. Atampore, J. Dingel and K. Rudie, A Controller Synthesis Framework for Automated Service CompositionJournal of Discrete Event Dynamic Systems:  Theory and Applications, Volume 29, Issue 3, pp. 297-365, 2019.
  • B. Behinaein, F. Lin and K. Rudie, Optimal Information Release for Mixed Opacity in Discrete-Event SystemsIEEE Transactions on Automation Science and Engineering, Volume 16, Number 4, pp. 196-1970, 2019.
  • D. Sears and K. Rudie, Computing Observers from Observation Policies in Discrete-Event Systems, Journal of Discrete Event Systems: Theory and Applications, Volume 28, Number 4, pp. 509-537, 2018.
  • W.M. Wonham, K. Cai and K. Rudie, Supervisory Control of Discrete-Event Systems: A Brief History, Annual Reviews in Control, Volume 45, pp. 250-256, 2018.
  • B. Behinaein, K. Rudie and W. Sangrar, Petri Net Siphon Analysis and Graph Theoretic Measures for Identifying Combination Therapies in Cancer, IEEE/ACM Transactions on Computational Biology and Bioinformatics, Volume 15, Number 1, pp. 231-243, 2018.
  • F. Atampore, J. Dingel and K. Rudie, Supervisor Aware Service Composition Framework: An Implementation and Evaluation, in Proceedings of the 14th International Workshop on Discrete Event Systems, Sorrento Coast, Italy, May 30-June 1, pp. 288-295, 2018.
  • S. Sikdar, S. Givigi and K. Rudie, A Resource Allocation Mechanism Using Matching and Bargaining, IEEE Transactions on Automatic Control, Volume 62, Number 11, pp. 5909-5914, 2017.
  • M.T.B. Waez, A. Wasowski, J. Dingel and K. Rudie, Controller Synthesis for Dynamic Hierarchical Real-Time Plants Using Timed Automata, Journal of Discrete Event Dynamic Systems: Theory and Applications, Volume 27, pp. 407-441, 2017.
  • D. Sears and K. Rudie, Minimal Sensor Activation and Minimal Communication in Discrete-Event Systems, Journal of Discrete Event Systems: Theory and Applications, Volume 26, Number 2, pp. 295-349, 2016.
  • F. Atampore, J. Dingel and K. Rudie, Towards Smart Services: A Controller Synthesis Framework for Automated Service Composition, poster at the 26th Centre for Advanced Studies Conference (CASCON), Toronto, October 31-November 2, 2016.
  • S.-J. Whittaker, K. Rudie and J. McLellan, An Augmented Petri Net Model for Health-Care Protocols, IEEE Transactions on Automatic Control, Volume 60, Number 9, pp. 2362-2377, 2015.
  • F. Atampore, J. Dingel and K. Rudie, Applying Control Synthesis to Web Service Composition, poster at the 25th Centre for Advanced Studies Conference (CASCON), Toronto, November 2-4, 2015.
  • U. Raza, E. Morin, K. Rudie and D. Maslove, An Investigation into Using Pulse Rate Variability as a Predictive Feature for Clinical Events, poster at the World Congress on Medical Physics and Biomedical Engineering, Toronto, Canada, June 7-12, 2015.
  • U. Raza, K. Rude, E. Morin, G. Palmer and S. Hunt, A CPX System for Remote Monitoring of Human Metabolic Rate Via the Cellular Network, poster at the American College of Sports Medicine 62nd Annual Meeting, San Diego, USA, May 2015.
  • M. T. B. Waez, A. Wasowski, J. Dingel, and K. Rudie, A Model for Industrial Real-Time Systems, in Proceedings of the International Conference on Verification, Model Checking and Abstract Interpretation (VCMAI), Mumbai, India, January 12-14, pp. 153-171, 2015.
  • D. Sears and K. Rudie, On Computing Indistinguishable States of Nondeterministic Finite Automata, in Proceedings of the IEEE Conference on Decision and Control, Los Angeles, pp. 6731-6736, 2014.
  • M.T.B. Waez, A. Wasowski, J. Dingel, and K. Rudie, Synthesis of a Reconfiguration Service for Mixed-Criticality Multi-Core Systems: An Experience Report, in Proceedings of the 11th International Symposium on Formal Aspects of Component Software, Bertinoro, Italy, 2014.
  • A. Auer, J. Dingel, and K. Rudie, Concurrency Control Generation for Dynamic Threads Using Discrete-Event Systems, Science of Computer Programming, Volume 82, pp. 22-43, 2014.
  • B. Behinaein , K. Rudie, and W. Sangrar, Structural Analysis of Petri Nets for Modeling and Analyzing Signaling Pathways, Proceedings of the Canadian Conference on Electrical and Computer Engineering (CCECE), Toronto, Canada, May 4-7, pp. 476-481, 2014.
  • S. Sikdar and K. Rudie, A Decentralised Electricity Market Model: An Electric Vehicle Charging Example, Proceedings of the Canadian Conference on Electrical and Computer Engineering (CCECE), Toronto, Canada, May 4-7, pp. 522-526, 2014.
  • M. T. B. Waez, J. Dingel, and K. Rudie, A Survey of Timed Automata for the Development of Real-Time Systems, Computer Science Review, Volume 9, pp. 1-26, 2013.
  • C. Winacott, B. Behinaein, and K. Rudie, Methods for the Estimation of the Size of Lookahead Tree State-Space, Journal of Discrete Event Dynamic Systems: Theory and Applications, Volume 23, Issue 2, pp. 135-155, June 2013.
  • D. Sears and K. Rudie, Computing Sensor Activation Decisions from State Equivalence Classes in Discrete-Event Systems, Proceedings of the IEEE Conference on Decision and Control, pp. 6972-6977, 2013.
  • D. Sears and K. Rudie, Efficient Computation of Sensor Activation Decisions in Discrete-Event Systems, Proceedings of the IEEE Conference on Decision and Control, pp. 6966-6971, 2013.
  • S. Sikdar and K. Rudie, Microgrid Level Competitive Market Using Dynamic Matching”, Electrical Power and Energy Conference (EPEC), Halifax, August 21-23, pp. 1-6, 2013.
  • N. Chausse, H. Xu, J. Dingel and K. Rudie, Combining Model Checking and Discrete-Event Supervisor Synthesis, Proceedings of the 11th International Workshop on Automated Verification of Critical Systems (AVoCS), Volume 46, 2011
  • L. Grigorov and K. Rudie, Dynamic Discrete-Event Systems with Instances for the Modelling of Emergency Response Protocols, Proceedings of the American Control Conference, San Francisco, CA, June 29-July 1, pp. 4478-4483, 2011.
  • L. Grigorov, B. Butler, J.E.R. Cury and K. Rudie, Conceptual Design of Discrete-Event Systems Using Templates, Journal of Discrete Event Dynamic Systems: Theory and Applications, Volume 21, Issue 2, pp. 257-303, June 2011.
  • L. Grigorov and K. Rudie, Techniques for the Parametrization of Discrete-Event System Templates, International Workshop on Discrete Event Systems (WODES), Berlin, Germany, August 30-September 1, pp. 380-385, 2010.
  • S.-J. Whittaker, K.Rudie, J. McLellan and S. Haar, Augmenting Petri Nets to Model Health-Care Protocols, International Workshop on Discrete Event Systems (WODES), Berlin, Germany, August 30-September 1, pp. 380-385, 2010.
  • M. Greenspan, K. Rudie, S. Simmons, Introducing Computer Programming with Lego Robotics, Proceedings of the Canadian Engineering Education Association, Kingston, June 7-9, 2010, Paper 3076 in Proceedings (no page numbers in electronic proceedings).
  • S.-J. Whittaker, K. Rudie, J. McLellan, and S. Haar, Choice-Point Nets: A Discrete-Event Modelling Technique for Analyzing Health Care Protocols, Proceedings of the Allerton Conference on Communication, Control and Computing, Monticello, Illinois, September 30-October 2, pp. 652-659, 2009.
  • A. Auer, J. Dingel and K. Rudie, Concurrency Control Generation for Dynamic Threads Using Discrete-Event Systems, in Proceedings of the 47th Annual Allerton Conference on Communication, Control, and Computing, Monticello, IL, Sept. 30 - Oct. 2, pp. 927-934, 2009.
  • C. Winacott and K. Rudie, Limited Lookahead Supervisory Control of Probabilistic Discrete-Event Systems, in Proceedings of the 47th Annual Allerton Conference on Communication, Control, and Computing, Monticello, IL, Sept. 30 - Oct. 2, pp. 660-667, 2009.
  • S.-J. Whittaker, K. Rudie, J. McLellan and S. Haar, Choice-Point Nets: A Discrete-Event Modelling Technique for Analyzing Health Care Protocols, in Proceedings of the 47th Annual Allerton Conference on Communication, Control, and Computing, Monticello, IL, Sept. 30 - Oct. 2, pp. 652-659, 2009.
  • L. Grigorov, Observations on Solving Discrete-Event Control Problems: Patterns and Strategies, Technical Report 2009-558, School of Computing, Queen's University, Canada, 2009.
  • C. Dragert, J. Dingel and K. Rudie, Generation of Concurrency Control Code Using Discrete-Event Systems Theory, in Proceedings of the 16th International Symposium on the Foundations of Software Engineering, Atlanta, GA, November 11-13, pp. 146-157, 2008.
  • S.-J. Whittaker and K. Rudie, Lose Fat, Not Muscle: An Examination of Supervisor Reduction in Discrete-Event Systems, Journal of Discrete Event Dynamic Systems, Vol. 18, No. 3, pp. 285-321, 2008.
  • Y. Huang, K. Rudie, and F. Lin, Decentralized Control of Discrete-Event Systems When Supervisors Observer Particular Event Occurrences, IEEE Transactions on Automatic Control, Vol. 53, Issue 1, pp. 384-388, 2008.
  • L. Grigorov, J.E.R. Cury and K. Rudie, Design of Discrete-Event Systems Using Templates, in Proceedings of the American Control Conference, Seattle, WA, June 11-13, pp. 499-504, 2008.
  • T. Brunsch and K. Rudie, Discrete-Event Systems Model of an Outbreak Response, in Proceedings of the American Control Conference, Seattle, WA, June 11-13, pp. 1709-1714,2008.
  • L. Grigorov, J.E.R. Cury, K. Rudie, and S. Klinge, Template Design and Automatic Generation of Controllers for Industrial Robots, in Proceedings of 23rd Annual ACM Symposium on Applied Computing (SAC), Fortaleza, Brazil, March 16-20, pp. 1612-1613, 2008.
  • S.-J. Whittaker, M. Zulkernine, and K. Rudie. Towards Incorporating Discrete-Event Systems in Secure Software Development, in Joint Proceedings of the International Conference on Availability, Reliability and Security( ARES) / International Conference on Complex, Intelligent, and Software Intensive Systems (CISIS) (IEEE Computer Society), Barcelona, Spain, March 4-7, pp. 1188-1195, 2008.
  • S. Blouin, M. Guay, and K. Rudie, An Application of Discrete-Event Theory to Truck Dispatching, Central European Journal of Operations Research (Springer), Vol. 15, Issue 4, pp. 369-391, 2007.
  • F. Lin, K. Rudie and S. Lafortune, Minimal Communication for Essential Transitions in a Distributed Discrete-Event System, IEEE Transactions on Automatic Control, Volume 52, Number 8, pp. 1495-1502, Aug. 2007.
  • L. Grigorov and K. Rudie, Problem Solving in Control of Discrete-Event Systems, in Proceedings of the European Control Conference, Kos, Greece, pp. 5500-5507, July 2-5, 2007.
  • S.-J. Whittaker and K. Rudie, Plug and Play: Modular Supervisor Reduction in Discrete-Event Systems, in Proceedings of the European Control Conference, Kos, Greece, pp. 4976-4983, July 2-5, 2007.
  • S. L. Ricker and K. Rudie, Knowledge is a Terrible Thing to Waste: Using Inference in Discrete-Event Control Problems, IEEE Transactions on Automatic Control, Volume 52, Number 3, pp. 428-441, 2007.
  • L. Grigorov and K. Rudie, Near-Optimal Online Control of Dynamic Discrete-Event Systems, Journal of Discrete Event Dynamic Systems: Theory and Applications, Volume 16, pp. 419-449, 2006.
  • Y. Huang, K. Rudie and F. Lin, Decentralized Control of Discrete-Event Systems When Supervisors Observe Particular Event Occurrences, in Proceedings of the American Control Conference, Minneapolis, MN, pp. 4147-4152, June 14-16, 2006.
  • K. Edlund, A. G. Michelsen and K. Rudie. Supervisory Control of Flowlines by Modelling the Legal Language as Inequalities, in Proceedings of the 8th International Workshop on Discrete Event Systems (WODES), Ann Arbor, MI, pp. 15-20, July 10-12, 2006.
  • L. Grigorov and K. Rudie, Issues in Optimal Control of Dynamic Discrete-Event Systems, in Proceedings of the 16th IFAC World Congress, Prague, July 4-8, 2005. (pdf version)(corresponding ppt)
  • I. Romanovski, M. Guay and K. Rudie, On the Supervisory Control for State Trajectory Specifications in Time-Varying Discrete-Event Systems, in Proceedings of the 16th IFAC World Congress, Prague, July 4-8, 2005.
  • K. Rudie, S. Lafortune, F. Lin, Minimal Communication in a Distributed Discrete-Event System, IEEE Transactions on Automatic Control, Volume 48, Number 6, pp. 957-975, 2003.
  • K. Rudie, How to be an Engineering Professor Yesterday, IEEE Control Systems Magazine, Volume 23, Number 3, pp. 10-11, 2003.
  • M. Aghamirian, K. Rudie, A. Burns, and G. Frontini, Using Timed Discrete-Event Systems and Discrete-Event Simulation to Design Control Policies in a Manufacturing System, in Proceedings of the 17th International Conference on Production Research, Blacksburg, VA, August 3-7, 2003.
  • S. Blouin, M. Guay and K. Rudie, Discrete Abstractions for Two-dimensional Nearly Integrable Continuous Systems, IFAC Conference on Analysis and Design of Hybrid Systems, June 16-18 2003, pp.383-388.
  • S.L. Ricker and K. Rudie, Knowledge is a Terrible Thing to Waste: Using Inference in Discrete-Event Control Problems, in Proceedings of the American Control Conference (ACC), Denver, CO, June 4-6, pp. 2246-2251, 2003.
  • S. Blouin, M. Guay, and K. Rudie, Discrete Abstractions for Nearly Integrable Continuous Systems: The Two Dimensional Case, International Journal of Hybrid Systems, Volume 2, Number 4, pp. 297-335, 2002.
  • E. Lemch, M. Guay, and K. Rudie, Modelling of Oil Production Operation in the Framework of Hybrid Systems, in Proceedings of the IEEE Conference on Decision and Control (CDC), Las Vegas, NV, December 10-13, pp. 1595-1600, 2002.
  • K. Rudie, The Current State of Decentralized Discrete-Event Control Systems, in Proceedings of the Mediterranean Conference on Control and Automation, Lisbon, Portugal, July 9-12, 2002.
  • S. Blouin, M. Guay, and K. Rudie, An Application of Discrete-Event Theory to Truck Dispatching, in Proceedings of the American Control Conference (ACC), Arlington, VA, June 25-27, pp. 2315-2320, 2001.
  • S.L. Ricker and K. Rudie, Distributed Knowledge for Communication in Decentralized Discrete-Event Systems, in Proceedings of the IEEE Conference on Decision and Control (CDC), Sydney, Australia, December 12-15, pp. 9-15, 2000.
  • S.L. Ricker and K. Rudie, Know Means No: Incorporating Knowledge into Discrete-Event Control Systems, IEEE Transactions on Automatic Control, Volume 45, Number 9, pp. 1656-1668, 2000.
  • G. Labinaz, M.M. Bayoumi, and K. Rudie, Viable Cascade Control and Application to a Batch Polymerization Process , IEEE Transactions on Control Systems Technology , Volume 8, Number 3, pp. 396-407, 2000.
  • S.L. Ricker and K. Rudie, Incorporating Communication and Knowledge into Decentralized Discrete-Event Systems, in Proceedings of the IEEE Conference on Decision and Control (CDC), Phoenix, AZ, December 7-10, pp. 1326-1332, 1999.
  • K. Rudie, S. Lafortune, and F. Lin, Minimal Communication in a Distributed Discrete-Event Control System, in Proceedings of the American Control Conference (ACC), San Diego, CA, June 2-4, pp. 1965-1970, 1999.
  • G. Labinaz, M.M. Bayoumi, and K. Rudie, A Survey of Modeling and Control of Hybrid Systems, Annual Reviews in Control, Volume 21, pp. 79-92, 1997.
  • S.L. Ricker, N. Sarkar, and K. Rudie, A Discrete-Event Systems Approach to Modeling Dextrous Manipulation, Robotica, Volume 14, pp. 515-525, 1996.
  • G. Labinaz, M.M. Bayoumi, and K. Rudie, Modeling and Control of Hybrid Systems: A Survey, in Proceedings of the IFAC World Congress , Volume J, July 1-5, pp. 293-304, 1996.
  • G. Labinaz, K. Rudie, L. Ricker, N. Sarkar, and M.M. Bayoumi, A Hybrid System Investigation of Fluid-Filled Tanks, Technical Report No. 96-01, Department of Electrical and Computer Engineering, Queen's University, Kingston, ON, 1996. Also presented at Mathematical Theory of Networks and Systems (MTNS) , St. Louis, MO, June 24-28, 1996.
  • K. Rudie and J.C. Willems, The Computational Complexity of Decentralized Discrete-Event Control Problems, IEEE Transactions on Automatic Control, Volume 40, Number 7, pp. 1313-1319, 1995.
  • K. Rudie, N. Shimkin, and S.D. O'Young, Timed Discrete-Event Systems: A Manufacturing Application, in Proceedings of the Conference on Information Sciences and Systems (CISS) , Volume I, Princeton, NJ, March 16-18, pp. 374-381, 1994.
  • K. Rudie and W.M. Wonham, Think Globally, Act Locally: Decentralized Supervisory Control, IEEE Transactions on Automatic Control , Volume 37, Number 11, pp. 1692-1708, 1992. Reprinted in SPIE Milestone Series, Volume MS 124, Selected Papers on Sensor and Data usion , Edited by F. Sadjadi, pp. 206-222, 1996.
  • K. Rudie and W.M. Wonham, Protocol Verification Using Discrete-Event Systems, in Proceedings of the IEEE Conference on Decision and Control (CDC) , Tucson, AZ, December 16-18, pp. 3770-3777, 1992.
  • K. Rudie and W.M. Wonham, The Infimal Prefix-Closed and Observable Superlanguage of a Given Language, Systems & Control Letters , Volume 15, pp. 361-371, 1990.
  • K. Rudie and W.M. Wonham, Supervisory Control of Communicating Processes, in Protocol Specification, Testing, and Verification, X , L. Logrippo, R. L. Probert and H. Ural (eds.), Elsevier Science Pub. (North-Holland), pp. 243-257, 1990. Presented at IFIP Tenth International Symposium on Protocol Specification, Testing, and Verification , Ottawa, ON, 1989.


Graduate Student Thesis Titles

  • V. Tolls, An Event-Based Approach to Modeling Complex Data in Critical Care, M.Sc. thesis, School of Computing, Queen's University, Kingston, Canada, February, 2018. Available here
  • D. Sears, Dynamic Observation in Discrete-Event Systems, Ph.D. thesis, School of Computing, Queen's University, Kingston, Canada, February, 2018. Available here
  • F. Atampore, Towards Provably Correct Services: Automated Service Composition Via Supervisory Control Synthesis, Ph.D. thesis, School of Computing, Queen's University, Kingston, Canada, September, 2017. Available here
  • B. Behinaein Hamgini, Petri Net Simphon Analysis and Network Centrality Measures for Identifying Combination Therapies in Signaling Pathways, Ph.D. thesis, Department of Electrical and Computer Engineering, Queen's University, Kingston, Canada, September, 2016. Available here
  • S. Sikdar, Many-to-Many Allocations in Systems of Self-Insterested Agents: Some Dominant Strategy Solutions, Ph.D. thesis, Department of Electrical and Computer Engineering, Queen's University, Kingston, Canada, January, 2016. Available here
  • M.T.B. Waez, A Model for Hierarchical Open Real-Time Systems, Ph.D. thesis, School of Computing, Queen's University, Kingston, Canada, September, 2015. Available here
  • C. Winacott, Limited Lookahead Control of Discrete-Event Systems: Cost, Probability and State Space, Master's thesis, School of Computing, Queen's University, Kingston, Canada, January, 2012. Available here
  • S.-J. Whittaker, Augmenting Petri Nets to Model Health-Care Protocols, Ph.D. thesis, School of Computing, Queen's University, Kingston, Canada, September, 2011. Available here
  • A. R. Auer, Using Discrete-Event Systems for the Automatic Generation of Concurrency Control for Dynamic Threads, Master's thesis, School of Computing, Queen's University, Kingston, Canada, May 2010. (pdf version)
  • L. G. Grigorov, Conceptual Design of Discrete-Event Systems Using Templates, Ph.D. thesis, School of Computing, Queen's University, Kingston, Canada, August 2009. (pdf version)
  • C.W.A. Dragert, Generation of Concurrency Controls Using Discrete-Event Systems , Master's thesis, School of Computing, Queen's University, Kingston, Canada, August 2008. (pdf version)
  • M. M. Wood, "Application, Implementation and Integration of Discrete-Event Systems Control Theory", Master's thesis, Department of Electrical and Computer Engineering, Queen's University, Kingston, Canada, August 2005. (pdf version)
  • S.-J. Whittaker, Does Size Matter? The Effects of Supervisor Reduction on Minimal Communication Between Distributed Discrete-Event Agents, Master's thesis, School of Computing, Queen's University, Kingston, Canada, August 2005. (pdf version)
  • Y. Huang, Transition-Based Coobservability in Distributed Discrete-Event Systems, Master's thesis, Department of Electrical and Computer Engineering, Queen's University, Kingston, Canada, 2005. (pdf version)
  • L. G. Grigorov, Control of Dynamic Discrete-Event Systems, Master's thesis, School of Computing, Queen's University, Kingston, Canada, 2004. (pdf version)
  • S. Blouin, Finite-state Machine Abstractions of Continuous Systems, Ph.D. thesis, Chemical Engineering Department, Queens University, Kingston, Canada, October 2003. (pdf version)
  • Arezou Mohammadi, "Sequences that Lead to Failure in Decentralized Supervisory Control, Master's Thesis, Queens University, Kingston, Canada, 2003.
  • H. Tun, Communication States in Decentralized Discrete-Event Systems, Master's thesis, Queens University, Kingston, Canada, May 2002.
  • S. Luo, A Systematic Method to Analyze Cryptographic Protocols using Discrete-Event Systems, Master's Thesis, Queens University, Kingston, Canada, September 1999. (pdf version)
  • L. Ricker, Knowledge and communication in decentralized discrete-event control, Ph.D. Thesis, Queens University, Kingston, Canada, 1999. (pdf version)
  • Adrian Payne, Matrix-Based Algorithms and an Analysis of System Structure for Partially-Observable Discrete-Event Systems, Master's Thesis, Queens University, Kingston, Canada, 1997.
Zahra's Convocation November 2019
Zahra Abedi Khouzani's convocation gives the QDES lab a chance to have a nice group photo (including a couple of others close to Zahra).
Jeremy wins FEAS poster award October 2019
Jeremy Kulchyk wins Best Poster Award at Queen's 2019 FEAS Research Symposium.
Improbable Escapes June 2019
DESlab celebrates the visit of Rômulo Meira Goes with a visit to Improbable Escapes. Our team manages to escape under the hour....with only a minute to spare.
Richard at Canadian AI Conf May 2019
Richard Moulton presenting at Canadian AI Conference, where he won the Canadian Artificial Intelligence Association's 2019 AI Master's Thesis Award.
IEEE Fellow January 2018
Karen Rudie named IEEE Fellow and is featured in the Queen's Gazette.

About IDES

IDES (Integrated Discrete-Event Systems) Software is designed to assist you with discrete-event problem-solving and with input and output of DES models. IDES allows you to mimic pen-and-paper drawing of state-transition diagrams, export your drawings to formats such asEPS, PNG, JPEG, LaTeX, or Grail+  and perform DES operations. It was created in the QDES Lab at Queen's University under the supervision of Prof. Karen Rudie. IDES is the product of many developers: Philippe Nguyen, Mike Wood, Lenko Grigorov, Kristian Edlund, Axel G. Michelsen, Helen Bretzke, Sarah-Jane Whittaker, Chris McAloney, Christian Silvano, Chris Dragert, Utsav Mital and Valerie Sugarman.

Github Project

Starting with version 3.1, the IDES source code was released under the AGPL-3.0 open source license and the project was moved to Github: https://github.com/krudie/IDES

Previous releases of IDES can be downloaded from the links below.

Contact Us

If you have questions or comments about IDES, we are best contacted via email. Please note that a reply may not be immediate.

Karen Rudie karen [.] rudie [at] queensu [.] ca
Lenko Grigorov lenko.grigorov [at] banica [.] org


 

IDES Previous Releases

The previous releases of IDES are for educational purposes only; to use our software, you must abide by the terms and conditions of the license. CLICK HERE to view the agreement.

IDES 3 beta 1

CLICK HERE to download the IDES3b1 zip package. After the download is complete, extract it in any location on your hard drive. A folder, called IDES3, will be created which contains all program files. Double-click on the IDES3.jar file inside this folder to launch the program. If "jar" files are not associated with Java on your machine, you may need to start a command prompt in the IDES folder and execute java -jar IDES3.jar to launch the program.

In order to use the LaTeX features of IDES, you have to install LaTeX and GhostScript on your computer. Full instructions on how to download and install this software can be found here.

Our software has a pluggable architecture that allows you to write your own features and to tailor IDES to your own DES needs. CLICK HERE to download the IDES3b1api developer add-on which contains the API, additional documentation and guide on writing plugins. This package is not required for regular users, only those that wish to develop their own IDES functionality.

IDES 2.1 beta 5

To download the previous incarnation IDES2.1b5, CLICK HERE. If you're looking for an even earlier version, please email us and we will provide you with a ZIP file.

 

IDES 3 Beta 1 Tutorial

A complete tutorial which describes how to use IDES can be found here. It will provide you with the overview necessary to begin drawing and manipulating finite-state machines, performing operations and more. It should be noted that our current release of IDES is a beta version and thus does not possess all the functionality it will in the future. The operations currently offered by IDES have been moderately tested, but our process of formal verification is not yet complete.

IDES 3 Beta 1 Release Notes

Known issues

  • Poor automatic placement of event labels on edges
  • Occasional poor automatic placement of edges
  • Node labels may not be centered properly when exporting to LaTeX or EPS
  • Potential problems when using the uniform node size option
  • DES operations are not formally verified
  • Automatic layout of the result of operations is slow
  • Pasting from the clipboard might not always work as expected

Changes from previous releases

Version: 3 beta 1

  • Numerous new operations
  • Multiple inputs can be selected for operations which support this (e.g., "sync")
  • New model type "Event Set"
  • Introduced an API for plugins. One can create plugins for custom
    • operations
    • import/export
    • graph layout
    • etc.
    (please download the developers package for relevant documentation)
  • The "Template Design" plugin is included with IDES
  • Event list is now visible in the side panel
  • Font size can be changed
  • Copy and paste of graphs and events is supported
  • Addition of a new tree layout algorithm
  • Tutorials included with IDES (listed in the Help menu)
  • Models can be annotated with arbitrary text ("Annotations" tab)
  • Warning and error messages appear in a separate "Notices" tab
  • Added command to simplify state labels
  • Examples are now included with IDES
  • Numerous bugfixes

Version: 2.1 beta 5

  • Fix to "supcon" operation
  • Fix to FSA implementation bug which could lead to incorrect DES operation results
  • Other minor bugfixes

Version: 2.1 beta 4

  • Introduction of Undo and Redo
  • New appearance of edges depending on controllability and observability. Controllable edges have a little marker, unobservable edges are dashed
  • Models can be renamed
  • New export to JPEG and PNG files
  • Fix to export to EPS
  • "Use uniform node size" is now graph-specific
  • IDES now remembers your interface settings, such as viewed portion of the model, zoom level, etc., when switching between models
  • Addition of the Multi-Agent product operation
  • "Filmstrip" at the bottom automatically scrolls to active model
  • Numerous bugfixes

Version: 2.1 beta 3

  • Greater usability when drawing graphs
  • Performance improvements (speed and memory footprint)
  • Large graphs with more than 100 states are not displayed graphically by default
  • New I/O subsystem
  • Automatic labeling of nodes
  • New "save modified models" dialog
  • Import/export of TCT and Grail+ files
  • Resolved occasional issues with the labelling of nodes after composition operations (e.g., synchronous product)
  • Smaller default node size so graphs look nicer
  • Compatibility issues with newer versions of MikTeX resolved
  • Improvements to the UI under MacOS
  • Numerous bugfixes