ing WS1S Systems to Verify Parameterized Networks . . . . . . . . . . . . 188 Kai Baukus, Saddek Bensalem, Yassine Lakhnech and Karsten Stahl FMona: A Tool for Expressing Validation Techniques over Infinite State Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204 J.-P. Bodeveix and M. Filali Transitive Closures of Regular Relations for Verifying Infinite-State Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220 Bengt Jonsson and Marcus Nilsson Diagnostic and Test Generation Using Static Analysis to Improve Automatic Test Generation . . . . . . . . . . . . . 235 Marius Bozga, Jean-Claude Fernandez and Lucian Ghirvu Efficient Diagnostic Generation for Boolean Equation Systems . . . . . . . . . . . . 251 Radu Mateescu Efficient Model-Checking Compositional State Space Generation with Partial Order Reductions for Asynchronous Communicating Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266 Jean-Pierre Krimm and Laurent Mounier Checking for CFFD-Preorder with Tester Processes . . . . . . . . . . . . . . . . . . . . . . . 283 Juhana Helovuo and Antti Valmari Fair Bisimulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299 Thomas A. Henzinger and Sriram K. Rajamani Integrating Low Level Symmetries into Reachability Analysis . . . . . . . . . . . . . 315 Karsten Schmidt Model-Checking Tools Model Checking Support for the ASM High-Level Language . . . . . . . . . . . . . . 331 Giuseppe Del Castillo and Kirsten Winter Table of

Tools and Algorithms for the Construction and Analysis of Systems. Proc. TACAS 2009

Journal of the ACM

In online advertising, response prediction is the problem of estimating the probability that an advertisement is clicked when displayed on a content publisher's webpage In this paper, we show how response prediction can be viewed as a problem of matrix completion, and propose to solve it using matrix factorization techniques from collaborative filtering (CF) We point out the two crucial differences between standard CF problems and response prediction, namely the requirement of predicting probabilities rather than scores, and the issue of confidence in matrix entries We address these issues using a matrix factorization analogue of logistic regression, and by applying a principled confidence-weighting scheme to its objective We show how this factorization can be seamlessly combined with explicit features or side-information for pages and ads, which let us combine the benefits of both approaches Finally, we combat the extreme sparsity of response prediction data by incorporating hierarchical information about the pages and ads into our factorization model Experiments on three very large real-world datasets show that our model outperforms current state-of-the-art methods for response prediction

/pdf/response-prediction-using-collaborative-filtering-with-2vcu6nl6iy.pdf

Response prediction using collaborative filtering with hierarchies and side-information

Combinatorics on words: a tutorial.

A growing trend in commercial search engines is the display of specialized content such as news, products, etc. interleaved with web search results. Ideally, this content should be displayed only when it is highly relevant to the search query, as it competes for space with "regular" results and advertisements. One measure of the relevance to the search query is the click-through rate the specialized content achieves when displayed; hence, if we can predict this click-through rate accurately, we can use this as the basis for selecting when to show specialized content. In this paper, we consider the problem of estimating the click-through rate for dedicated news search results. For queries for which news results have been displayed repeatedly before, the click-through rate can be tracked online; however, the key challenge for which previously unseen queries to display news results remains. In this paper we propose a supervised model that offers accurate prediction of news click-through rates and satisfies the requirement of adapting quickly to emerging news events.

/pdf/click-through-prediction-for-news-queries-2t8k35495c.pdf

Click-through prediction for news queries

We define the notion of height-deterministic pushdown automata, a model where for any given input string the stack heights during any (nondeterministic) computation on the input are a priori fixed. Different subclasses of height-deterministic pushdown automata, strictly containing the class of regular languages and still closed under boolean language operations, are considered. Several such language classes have been described in the literature. Here, we suggest a natural and intuitive model that subsumes all the formalisms proposed so far by employing height-deterministic pushdown automata. Decidability and complexity questions are also considered.

/pdf/height-deterministic-pushdown-automata-k3uzrmvgdp.pdf

Height-deterministic pushdown automata

The study of word equations is a central topic in mathematics and theoretical computer science. Recently, the question of whether a given word equation, augmented with various constraints/extensions, has a solution has gained critical importance in the context of string SMT solvers for security analysis. We consider the decidability of this question in several natural variants and thus shed light on the boundary between decidability and undecidability for many fragments of the first order theory of word equations and their extensions. In particular, we show that when extended with several natural predicates on words, the existential fragment becomes undecidable. On the other hand, the positive \(\varSigma _2\) fragment is decidable, and in the case that at most one terminal symbol appears in the equations, remains so even when length constraints are added. Moreover, if negation is allowed, it is possible to model arbitrary equations with length constraints using only equations containing a single terminal symbol and length constraints. Finally, we show that deciding whether solutions exist for a restricted class of equations, augmented with many of the predicates leading to undecidability in the general case, is possible in non-deterministic polynomial time.

The Satisfiability of Word Equations: Decidable and Undecidable Theories

Pseudo-repetitions are a natural generalization of the classical notion of repetitions in sequences.
We solve fundamental algorithmic questions on pseudo-repetitions by application of insightful
combinatorial results on words. More precisely, we efficiently decide whether a word is a pseudorepetition and ﬁnd all the pseudo-repetitive factors of a word.

/pdf/finding-pseudo-repetitions-2q55cv7618.pdf

Finding Pseudo-Repetitions

Pseudo-repetitions are a natural generalisation of the classical notion of repetitions in sequences: they are the repeated concatenation of a word and its encoding under a certain morphism or antimorphism (anti-/morphism, for short). We approach the problem of deciding eciently, for a word w and a literal anti-/morphism f, whether w contains an instance of a given pattern involving a variablex and its image underf, i.e., f(x). Our results generalise both the problem of finding fixed repetitive structures (e.g., squares, cubes) inside a word and the problem of finding palindromic structures inside a word. For instance, we can detect eciently a factor of the form xx R xxx R , or any other pattern of such type. We also address the problem of testing eciently, in the same setting, whether the wordw contains an arbitrary pseudo-repetition of a given exponent. 1998 ACM Subject Classification F.2.2 Nonnumerical Algorithms and Problems

/pdf/testing-generalised-freeness-of-words-42cuofj59j.pdf

Testing Generalised Freeness of Words

A short proof is given for a result of Fraenkel and Simpson [Electronic J Combinatorics 2 (1995) #R2] stating that there exists an infinite binary word which has only three different squares u^2

http://eprints.uni-kiel.de/20546/1/FewSquares.pdf

Dirk Nowotka

Papers

Height-deterministic pushdown automata

The Satisfiability of Word Equations: Decidable and Undecidable Theories

Finding Pseudo-Repetitions

Testing Generalised Freeness of Words

Binary Words with Few Squares