Every day, we make sequences of decisions to accomplish our goals, and we attempt to achieve these goals in the most favorable way. In many aspects of life, such as in security or economy, the optimality of these decisions is critical, and a computational support for decision making is thus needed. Sequential decision making is, however, computationally challenging in the presence of uncertainty (partially observable Markov decision processes) or even adversaries (partially observable stochastic games). We provide a game theoretic model of one-sided partially observable stochastic games which is motivated by problems arising mainly in security. It captures both the uncertainty of the decision maker and the adversarial nature of the problem into account. Our framework assumes two players where one player is given the advantage of having perfect information. We show that we can solve such games in the similar fashion as one solves POMDPs using the value iteration algorithm, including its more practical approximate variants based on point-based updates of the value function.

Virtually all real-valued computations are carried out using floating-point data types and operations. With the current emphasis of system development often being on computational efficiency, developers as well as compilers are increasingly attempting to optimize floating-point routines. Reasoning about the correctness of these optimizations is complicated, and requires error analysis procedures with different characteristics and trade-offs. In my talk, I will motivate the need for such analyses. Then, I will present both a dynamic and a rigorous static analysis we developed for estimating errors of floating-point routines. Finally, I will describe how we extended our rigorous static analysis into a procedure for mixed-precision tuning of floating-point routines.

Short bio:

Zvonimir Rakamaric is an assistant professor in the School of Computing at the University of Utah. Prior to this, he was a postdoctoral fellow at Carnegie Mellon University in Silicon Valley, where he worked closely with researchers from the Robust Software Engineering Group at NASA Ames Research Center to improve the coverage of testing of NASA’s flight critical systems. Zvonimir received his bachelor’s degree in Computer Science from the University of Zagreb, Croatia; he obtained his M.Sc. and Ph.D. from the Department of Computer Science at the University of British Columbia, Canada.

Zvonimir‘s research mission is to improve the reliability and resilience of complex software systems by empowering developers with practical tools and techniques for analysis of their artifacts. He is a recipient of the NSF CAREER Award 2016, Microsoft Research Software Engineering Innovation Foundation (SEIF) Award 2012, Microsoft Research Graduate Fellowship 2008-2010, Silver Medal in the ACM Student Research Competition at the 32nd International Conference on Software Engineering (ICSE) 2010, and the Outstanding Student Paper Award at the 13th International Conference on Tools and Algorithms for the Construction and Analysis of Systems (TACAS) 2007.

For more information about Zvonimir, visit www.zvonimir.info.

Abstract:

Analyzing and reasoning about safety properties of software systems

becomes an especially challenging task for programs with complex flow

and, in particular, with loops or recursion. For such programs one needs

additional information, for example in the form of loop invariants,

expressing properties to hold at intermediate program points. We study

program loops with non-trivial arithmetic, implementing addition and

multiplication among numeric program variables. In this talk, we present

a new approach for automatically generating all polynomial invariants of

a class of such programs, based on techniques from computer algebra,

which will be explained thoroughly and intuitively.

Probabilistic programming is en vogue. It is used to describe

complex Bayesian networks, quantum programs, security protocols and

biological systems. Programming languages like C, C#, Java, Prolog,

Scala, etc. all have their probabilistic version. Key features are

random sampling and means to adjust distributions based on obtained

information from measurements and system observations. We show some

semantic intricacies, argue that termination is more involved than the

halting problem, and discuss recursion as well as run-time analysis.

Constrained counting and sampling are two fundamental problems in Computer Science with numerous applications, including network reliability, privacy, probabilistic reasoning, and constrained-random verification. In constrained counting, the task is to compute the total weight, subject to a given weighting function, of the set of solutions of the given constraints . In constrained sampling, the task is to sample randomly, subject to a given weighting function, from the set of solutions to a set of given constraints.

In this talk, I will introduce a novel algorithmic framework for constrained sampling and counting that combines the classical algorithmic technique of universal hashing with the dramatic progress made in Boolean reasoning over the past two decades. This has allowed us to obtain breakthrough results in constrained sampling and counting, providing a new algorithmic toolbox in machine learning, probabilistic reasoning, privacy, and design verification . I will demonstrate the utility of the above techniques on various real applications including probabilistic inference, design verification and our ongoing collaboration in estimating the reliability of critical infrastructure networks during natural disasters.

Bio:

Kuldeep Meel is a final year PhD candidate in Rice University working with Prof. Moshe Vardi and Prof. Supratik Chakraborty. His research broadly lies at the intersection of artificial intelligence and formal methods. He is the recipient of a 2016-17 IBM PhD Fellowship, the 2016-17 Lodieska Stockbridge Vaughn Fellowship and the 2013-14 Andrew Ladd Fellowship. His research won the best student paper award at the International Conference on Constraint Programming 2015. He obtained a B.Tech. from IIT Bombay and an M.S. from Rice in 2012 and 2014 respectively. He co-won the 2014 Vienna Center of Logic and Algorithms International Outstanding Masters thesis award.

Abstract:

In our project we are working on a framework that provides holistic security guarantees for web-based systems in which information flows heavily but not all flows should be allowed. As a case study we developed CoCon, a conference management system with verified document confidentiality. In my talk, I will start with a demo of CoCon, show which properties of the system we verified in the interactive theorem prover Isabelle and explain how we technically capture the intuitive idea that an attacker cannot learn any secrets of the system. A discussion of limitations of our approach will follow together with a summary of our experience with deployment of CoCon for real-life conferences. At the end, I will shortly mention future work.

Guarded protocols, as introduced by Emerson and Kahlon (2000), describe concurrent systems where transitions of processes are enabled or disabled depending on the existence of other processes in certain local states. Cutoff results reduce reasoning about systems with an arbitrary number of processes to systems of a determined, fixed size. Our work is based on the observation that the existing cutoff results are i) of limited use for liveness properties because the reductions do not preserve fairness, and ii) in many cases give a prohibitively large cutoff. We provide new cutoff results that work under fairness assumptions, and prove tightness or asymptotic tightness for cutoffs that only depend on the size of the process templates. I will also report on ongoing work to obtain smaller cutoffs by considering additional static properties of the process templates, such as the number of different guards that are used in the template.

Abstract:

We introduce a graphical syntax for signal flow diagrams based on the language of symmetric monoidal categories. Using universal categorical constructions, we provide a stream semantics and a sound and complete axiomatisation. A certain class of diagrams captures the orthodox notion of signal flow graph used in control theory; we show that any diagram of our syntax can be realised, via rewriting in the equational theory, as a signal flow graph.

Automata learning, or regular inference, is a widely used technique for creating an automaton model from observations. In recent years, it has been successfully applied to the verification of security protocols, hardware, and software systems. The original algorithm L* works for deterministic finite automata, and is only capable of learning control-flow models.

In this talk I will present an extension of L* to learn combined control/data-flow models in the form of nominal automata, which are acceptors of languages over infinite (structured) alphabets. After recalling L*, I will briefly present the theory of nominal sets. Then I will show how this theory enables extending L* to infinite alphabets in a seamless way, with almost no modifications to the original code. Finally, I will give a short demo of a tool based on this work, currently being developed at UCL.