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Text of the page (random words):
or a time step the natural generalization would be a game in which players could propose either a move or a time step yet we were unsatisfied with this model it seemed to us that it was different to say let me wait 14 seconds and reconvene then let me play my king of spades or let me play my king of spades in 14 seconds in the first by stopping after 14 seconds the player is providing a warning that the card might be played in the second there is no such warning in other words if players propose either a move or a time step they cannot take the adversary by surprise with a move at an unanticipated instant we wanted a model that could capture this element of surprise to capture the element of surprise we came up with a model in which players propose both a move and the delay with which it is played after this natural insight the difficulty was to find the appropriate winning condition so that a player could not win by stopping time tom besides the infinite state space region construction etc a second issue that is specific to timed systems is the divergence of time technically divergence is a built in büchi condition there are infinitely many clock ticks so all safety and reachability questions about timed systems are really co büchi and büchi questions respectively this observation had been part of my work on timed systems since the early 1990s but it has particularly subtle consequences for timed games where no player and no collaboration of players should have the power to prevent time from diverging this had to be kept in mind during the exploration of the modeling space all we came up with many possible winning conditions and for each we identified some undesirable property except for the one that we published this is in fact an aspect that did not receive enough attention in the paper we presented the chosen winning condition but we did not discuss in full detail why several other conditions that might have seemed plausible did not work in the process of analyzing the winning conditions we came up with many interesting games which form the basis of many results such as the result on lack of determinazation on the need for memory in reachability games even when clock values are part of the state and most famously as it gave the title to the paper on the power of surprise after this fun ride came the hard work where we had to figure out how to solve these games we had worked at symbolic approaches to games before and we followed the approach here but there were many complex technical adaptations required when we look at the paper in the distance of time it has this combination of a natural game model but also of a fairly sophisticated solution algorithm luca a and mickael did any of your subsequent research build explicitly on the results and the techniques you developed in your award winning paper if so which of your subsequent results on timed games do you like best is there any result obtained by other researchers that builds on your work and that you like in particular or found surprising luca marco and i built ticc which was meant to be a tool for timed interface theories based largely on the insights in this paper the idea was to be able to check the compatibility of real time systems and automatically infer the requirements that enable two system components to work well together to be compatible in time we thought this would be useful for hardware or embedded systems and especially for control systems and in fact the application is important there is now much successful work on the compositionality of stateflow simulink models we used mtbdds as the symbolic engine and marco and i invented a language for describing the components and we wrote by pair programming some absolutely beautiful ocaml code that compiled real time component models into mtbdds perhaps the nicest code i have ever written the problem was that we were too optimistic in our approach to state explosion and we were never able to study any system of realistic size after this i became interested in games more in an economic setting and from there i veered into incentive systems and from there to reputation systems and to a three year period in which i applied reputation systems in practice in industry thus losing somewhat touch with formal methods work marco i ve kept working on games since the award winning paper in one way or another the closest i ve come to the timed game setting has been with controller synthesis games for hybrid automata in a series of papers we had fun designing and implementing symbolic algorithms that manipulate polyhedra to compute the winning region of a linear hybrid game the experience gained on timed games helped me recognize the many subtleties arising in games played in real time on a continuous state space mariëlle i have been working on games for test case generation one player represents the tester which chooses inputs to test the other player represents the system under test and chooses the outputs of the system strategy synthesis algorithms can then compute strategies for the tester that maximize all kinds of objectives eg reaching certain states test coverage etc a result that i really like is that we were able to show a very close correspondence between the existing testing frameworks and game theoretic frameworks specifications act as game arenas test cases are exactly game strategies and the conformance relation used in testing namely ioco coincides with game refinement i e alternating refinement rupak in an interesting way the first paper on games i read was the one by maler pnueli and sifakis stacs 95 that had both fixpoint algorithms and timed games without surprise so the problem of symbolic solutions to games and their applications in synthesis followed me throughout my career i moved to finding controllers for games with more general non linear dynamics where we worked on abstraction techniques we also realized some new ways to look at restricted classes of adversaries i was always fortunate to have very good collaborators who kept my interest alive with new insights very recently i have gotten interested in games from a more economic perspective where players can try to signal each other or persuade each other about private information but it s too early to tell where this will lead luca a and mickael what are the research topics that you find most interesting right now is there any specific problem in your current field of interest that you d like to see solved mariëlle throughout my academic life i have been working on stochastic analysis with luca and marco we worked on stochastic games a lot first only on theory but later also on industrial applications esp in the railroad and high tech domain at some point in time i realized that my work was actually centred around analysing failure probabilities and risk that is how i moved into risk analysis the official title of the title of the chair i hold is risk management for high tech systems the nice thing is this sells much better than formal methods almost nobody knows what formal methods are and if they know people think yes those difficult people who urge us to specify everything mathematically for risk management this is completely different everybody understands that this is an important area luca i am currently working on computational ecology on ml for networks and on fairness in data and ml in computational ecology we are working on the role of habitat and territory for species viability we use ml techniques to write differentiable algorithms where we can compute the effect of each input such as the kind of vegetation in each square kilometer of territory on the output if all goes well this will enable us to efficiently compute which regions should be prioritized for protection and habitat conservation in networks we have been able to show that reinforcement learning can yield tremendous throughput gains in wireless protocols and we are now starting to work on routing and congestion control and in fairness and ml we have worked on the automatic detection of anomalous data subgroups something that can be useful in model diagnostics and we are now working on the spontaneous inception of discriminatory behavior in agent systems while these do not really constitute a coherent research effort i can certainly say that i am having a grand tour of cs the kind of joy ride one can afford with tenure rupak i have veered between practical and theoretical problems i am working on charting the decidability frontier for infinite state model checking problems most recently for asynchronous programs and context bounded reachability i am also working on applying formal methods to the world of cyber physical systems mostly games and synthesis finally i have become very interested in applying formal methods to large scale industrial systems through a collaboration with amazon web services there is still a large gap between what is theoretically understood and what is practically applicable to these systems and the problems are a mix of technical and social luca a and mickael you have a very strong track record in developing theoretical results and in applying them to real life problems in our admittedly biased opinion your work exemplifies ben schneiderman s twin win model which propounds the pursuit of the dual goals of breakthrough theories in published papers and validated solutions that are ready for widespread dissemination could you say a few words on your research philosophy how do you see the interplay between basic and applied research luca this is very kind for you to say and a bit funny to hear because certainly when i was young i had a particular talent for getting lost in useless theoretical problems i think two things played in my favor one is that i am curious the other is that i have a practical streak i still love writing code and tinkering with things from iot to biology to web and more this tinkering was at the basis of many of the works i did my work on reputation systems started when i created a wiki on cooking people were vandalizing it and i started to think about game theory and incentives for collaboration which led to my writing much of the code for wikipedia analysis and at google for maps edits analysis my work on networks started with me tinkering with simple reinforcement learning schemes that might work and writing the actual code on the flip side my curiosity too often had the better of me so that i have been unable to pay the continuous and devoted attention to a single research field i am not a specialist in any single thing i do or i have done i am always learning the ropes of something i don t quite know yet how to do my applied streak probably gave me some insight on which problems might be of more practical relevance and my frequent field changes have allowed me to bring new perspectives to old problems there were not many people using rl for wireless networks there are not many who write ml and gpu code and also avidly read about conservation biology rupak i must say that tom and luca were very strong influencers for me in my research both in problem selection and in appreciating the joy of research i remember one comment of tom paraphrased as life is short we should write papers that get read i spent countless hours in luca s office and learnt a lot of things about research coffee the ideal way to make pasta and so on marco it was an absolute privilege to be part of the group that wrote that paper my 4th overall according to dblp i d like to thank my coauthors and luca in particular for guiding me during those crucially formative years mariëlle i fully agree luca a and mickael several of you have high profile leadership roles at your institutions what advice would you give to a colleague who is about to take up the role of department chair director of a research centre dean or president of a university how can one build a strong research culture stay research active and live to tell the tale luca my colleagues may have better advice my productivity certainly decreased when i was department chair and is lower even now that i am the vice chair when i was young i was ambitious enough to think that my scientific work would have the largest impact among the things i was doing but i soon realized that some of the greatest impact was on others on my collaborators on the students i advised who went on to build great careers and stayed friends and on all the students i was teaching this awareness serves to motivate and guide me in my administrative work the cs department at ucsc is one of the ten largest in the number of students we graduate and the time i spend on improving its organization and the quality of the education it delivers is surely very impactful my advice to colleagues is to consider their service not as an impediment to research but as one of the most impactful things they do my way of staying alive is to fence off some days that i only dedicate to research aside from some unavoidable emergency and also to have collaborators that give me such joy in working together that they brighten and energize my whole day luca a and mickael finally what advice would you give to a young researcher who is keen to start working on topics related to concurrency theory today luca oh that sounds very interesting and may i show you this very interesting thing we are doing in jax to model bird dispersal we feed in this climate and vegetation data and then we just kidding just kidding if i come to concur i promise not to lead any of the concurrency yearlings astray at least i will try my main advice would be this work on principles that allow correct by design development if you look at programming languages and software engineering the progress in software productivity has not happened because people have become better at writing and debugging code written in machine language or c it has happened because of the development of languages and software principles that make it easier to build large systems that are correct by construction we need the same kind of principles modeling languages and ideas to build correct concurrent systems verification alone is not enough work on design tools ideas to guide design and design languages tom in concurrency theory we define formalisms and study their properties most papers do the studying not the defining they take a formalism that was defined previously by themselves or by someone else and study a property of that formalism usually to answer a question that is inspired by some practical motivation to me this omits the most fun part of the exercise the it defining part the point i am trying to make is not that we need more formalisms but that if one wishes to study a specific question it is best to study the question on the simplest possible formalism that exhibits exactly the features that make the question meaningful to do this one often has to define that formalism in other words the...