VSL 2014: VIENNA SUMMER OF LOGIC 2014
WST ON THURSDAY, JULY 17TH, 2014
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08:45-10:15 Session 62B: Non-Termination
Location: FH, Seminarraum 101B
08:45
Non-termination of Dalvik bytecode via compilation to CLP
SPEAKER: Fred Mesnard

ABSTRACT. We present a set of rules for compiling a Dalvik bytecode program into a logic program with array constraints. Non-termination of the resulting program entails that of the original one, hence the techniques we have presented before for proving non-termination of constraint logic programs can be used for proving non-termination of Dalvik programs.

09:15
Geometric Series as Nontermination Arguments for Linear Lasso Programs

ABSTRACT. We present a new kind of nontermination argument for linear lasso programs, called geometric nontermination argument. A geometric nontermination argument is a finite representation of an infinite execution of the form $(\vec{x} + \sum_{i=0}^t \lambda^i \vec{y})_{t \geq 0}$. The existence of this nontermination argument can be stated as a set of nonlinear algebraic constraints. We show that every linear loop program that has a bounded infinite execution also has a geometric nontermination argument. Furthermore, we discuss nonterminating programs that do not have a geometric nontermination argument.

09:45
Non-termination using Regular Languages
SPEAKER: unknown

ABSTRACT. We describe a method for proving non-termination of term rewriting systems that do not admit looping reductions, that is, reductions of the form $t \to^* C[t\sigma]$. As certificates of non-termination, we employ regular automata.

10:15-10:45Coffee Break
10:45-13:00 Session 66AI: Invited Talk and Imperative Programs
Location: FH, Seminarraum 101B
10:45
Termination of Biological Programs
SPEAKER: Jasmin Fisher

ABSTRACT. Living cells are highly complex reactive systems operating under varying environmental conditions. By executing diverse cellular programs, cells are driven to acquire distinct cell fates and behaviours. Deciphering these programs is key to understanding how cells orchestrate their functions to create robust systems in health and disease. Due to the staggering complexity, this remains a major challenge. Stability in biological systems is a measure of the homeostatic nature and robustness against environmental perturbations. In computer science, stability means that the system will eventually reach a fixed point regardless of its initial state. Or, in other words, that all computations terminate with variables acquiring the same value regardless of the path that led to termination. Based on robust techniques to prove stabilization/termination in very large systems, we have developed an innovative platform called BMA that allows biologists to model and analyse biological signalling networks. BMA analyses systems for stabilization, searches for paths leading to stabilization, and allows for bounded model-checking and simulation, all with intelligible visualization of results. In this talk, I will summarize our efforts in this direction and talk about the application of termination analysis in drug discovery and cancer.

Joint work with Byron Cook, Nir Piterman, Samin Ishtiaq, Alex Taylor and Ben Hall.

11:45
On Improving Termination Preservability of Transformations from Procedural Programs into Rewrite Systems by Using Loop Invariants
SPEAKER: Naoki Nishida

ABSTRACT. Recently, to analyze procedural programs by using techniques in the field of term rewriting, several transformations of a program into a rewrite system have been developed. Such transformations are basically complete in the sense of computation, and e.g., termination of the rewrite system ensures termination of the program. However, in general, termination of the program is not preserved by the transformations and, thus, the preservation of termination is a common interesting problem. In this paper, we discuss the improvement of a transformation from a simple procedural program over integers into a constrained term rewriting system by appending loop invariants to loop conditions of "while" statements so as to preserve termination as much as possible.

12:15
Automatic Termination Analysis for GPU Kernels
SPEAKER: Jeroen Ketema

ABSTRACT. We describe a method for proving termination of massively parallel GPU kernels. An implementation in KITTeL is able to show termination of 94% of the 598 kernels in our benchmark suite.

12:45
Discussion
SPEAKER: Everyone
13:00-14:30Lunch Break
14:30-16:00 Session 75AI: Ranking Functions and Complexity
Location: FH, Seminarraum 101B
14:30
To Infinity... and Beyond!

ABSTRACT. The traditional method for proving program termination consists in inferring a ranking function. In many cases (i.e. programs with unbounded non-determinism), a single ranking function over natural numbers is not sufficient. Hence, we propose a new abstract domain to automatically infer ranking functions over ordinals. We extend an existing domain for piecewise-defined natural-valued ranking functions to polynomials in $\omega$, where the polynomial coefficients are natural-valued functions of the program variables. The abstract domain is parametric in the choice of the state partitioning inducing the piecewise-definition and the type of functions used as polynomial coefficients. To our knowledge this is the first abstract domain able to reason about ordinals. Handling ordinals leads to a powerful approach for proving termination of imperative programs, which in particular allows us to take a first step in the direction of proving termination under fairness constraints and proving liveness properties of (sequential and) concurrent programs.

15:00
Real-world loops are easy to predict : a case study
SPEAKER: Laure Gonnord

ABSTRACT. In this paper we study the relevance of fast and simple solutions to compute approximations of the number of iterations of loops (loop trip count) of imperative real-world programs. The context of this work is the use of these approximations in compiler optimizations: most of the time, the optimizations yield greater benefits for large trip counts, and are either innocuous or detrimental for small ones. In this particular work, we argue that, although predicting exactly the trip count of a loop is undecidable, most of the time, there is no need to use computationally expensive state-of-the-art methods to compute (an approximation of) it. We support our position with an actual case study. We show that a fast predictor can be used to speedup the JavaScript JIT compiler of Firefox - one of the most well-engineered runtime environments in use today. We have accurately predicted over 85% of all the interval loops found in typical JavaScript benchmarks, and in millions of lines of C code. Furthermore, we have been able to speedup several JavaScript programs by over 5%, reaching 24% of improvement in one benchmark.

15:30
Type Introduction for Runtime Complexity Analysis
SPEAKER: unknown

ABSTRACT. In this note we show that the runtime complexity function of a sorted rewrite system R coincides with the runtime complexity function of the unsorted rewrite system obtained by forgetting sort information. Hence our result states that sort-introduction, a process that is easily carried out via unification, is sound for runtime complexity analysis. Our result thus provides the foundation for exploiting sort information in analysis of TRSs.

16:00-16:30Coffee Break
16:30-19:00 Session 79A: VSL Joint Award Ceremony 1
Location: MB, Kuppelsaal
16:30
Foundations and Technology Competitions Award Ceremony

ABSTRACT. The third round of the Kurt Gödel Research Prize Fellowships Program, under the title: Connecting Foundations and Technology, aims at supporting young scholars in early stages of their academic careers by offering highest fellowships in history of logic, kindly supported by the John Templeton Foundation. Young scholars being less or exactly 40 years old at the time of the commencement of the Vienna Summer of Logic (July 9, 2014) will be awarded one fellowship award in the amount of EUR 100,000, in each of the following categories:

• Logical Foundations of Mathematics,
• Logical Foundations of Computer Science, and
• Logical Foundations of Artificial Intelligence

The following three Boards of Jurors were in charge of choosing the winners:

• Logical Foundations of Mathematics: Jan Krajíček, Angus Macintyre, and Dana Scott (Chair).
• Logical Foundations of Computer Science: Franz Baader, Johann Makowsky, and Wolfgang Thomas (Chair).
• Logical Foundations of Artificial Intelligence: Luigia Carlucci Aiello, Georg Gottlob (Chair), and Bernhard Nebel.

http://fellowship.logic.at/

17:30
FLoC Olympic Games Award Ceremony 1

ABSTRACT. The aim of the FLoC Olympic Games is to start a tradition in the spirit of the ancient Olympic Games, a Panhellenic sport festival held every four years in the sanctuary of Olympia in Greece, this time in the scientific community of computational logic. Every four years, as part of the Federated Logic Conference, the Games will gather together all the challenging disciplines from a variety of computational logic in the form of the solver competitions.

At the Award Ceremonies, the competition organizers will have the opportunity to present their competitions to the public and give away special prizes, the prestigious Kurt Gödel medals, to their successful competitors. This reinforces the main goal of the FLoC Olympic Games, that is, to facilitate the visibility of the competitions associated with the conferences and workshops of the Federated Logic Conference during the Vienna Summer of Logic.

This award ceremony will host the

• 3rd Confluence Competition (CoCo 2014);
• Configurable SAT Solver Challenge (CSSC 2014);
• Ninth Max-SAT Evaluation (Max-SAT 2014);
• QBF Gallery 2014; and
• SAT Competition 2014 (SAT-COMP 2014).
18:15
FLoC Closing Week 1
SPEAKER: Helmut Veith
16:30-18:00 Session 80C: New Frontiers
Location: FH, Seminarraum 101B
16:30
Ordering Networks

ABSTRACT. This extended abstract discusses the problem of defining quasi-orders that are suitable for use with network rewriting.

17:00
Discussion
SPEAKER: Everyone