The Fractal Dimension of SAT Formulas

Modern SAT solvers have experienced a remarkable progress on solving industrial instances. Most of the techniques have been developed after an intensive experimental testing process. Recently, there have been some attempts to analyze the structure of these formulas in terms of complex networks, with the long-term aim of explaining the success of these SAT solving techniques, and possibly improving them. We study the fractal dimension of SAT formulas, and show that most industrial families of formulas are self-similar, with a small fractal dimension. We also show that this dimension is not affected by the addition of learnt clauses. We explore how the dimension of a formula, together with other graph properties can be used to characterize SAT instances. Finally, we give empirical evidence that these graph properties can be used in state-of-the-art portfolios.Comment: 20 pages, 11 Postscript figure

Community Structure in Industrial SAT Instances

Modern SAT solvers have experienced a remarkable progress on solving industrial instances. Most of the techniques have been developed after an intensive experimental process. It is believed that these techniques exploit the underlying structure of industrial instances. However, there are few works trying to exactly characterize the main features of this structure. The research community on complex networks has developed techniques of analysis and algorithms to study real-world graphs that can be used by the SAT community. Recently, there have been some attempts to analyze the structure of industrial SAT instances in terms of complex networks, with the aim of explaining the success of SAT solving techniques, and possibly improving them. In this paper, inspired by the results on complex networks, we study the community structure, or modularity, of industrial SAT instances. In a graph with clear community structure, or high modularity, we can find a partition of its nodes into communities such that most edges connect variables of the same community. In our analysis, we represent SAT instances as graphs, and we show that most application benchmarks are characterized by a high modularity. On the contrary, random SAT instances are closer to the classical Erd\"os-R\'enyi random graph model, where no structure can be observed. We also analyze how this structure evolves by the effects of the execution of a CDCL SAT solver. In particular, we use the community structure to detect that new clauses learned by the solver during the search contribute to destroy the original structure of the formula. This is, learned clauses tend to contain variables of distinct communities

The Impact of Implied Constraints on MaxSAT B2B Instances

The B2B scheduling optimization problem consists of finding a schedule of a set of meetings between pairs of participants, minimizing their number of idle time periods. Recent works have shown that SAT-based approaches are state-of-the-art on this problem. One interesting feature of such approaches is the use of implied constraints. In this work, we provide an experimental setting to study the impact of using these implied constraints in MaxSAT B2B instances. To this purpose and due to the reduced number of existing real-world B2B instances, we propose a random B2B instance generation model, which reproduces certain features of these problems. In our experimental analysis, we show that the impact of using some implied constraints in the MaxSAT encodings depends on the characteristics of the problem, and we also analyze the benefits of combining them. Finally, we give some insights on how a MaxSAT solver is able to exploit these implied constraints.Spanish Government RTI2018-095609-B-I00French National Research Agency (ANR) ANR-19-CHIA-0013-01Juan de la Cierva program - MCIN IJC2019040489-IAE

Characterizing the Temperature of SAT Formulas

The remarkable advances in SAT solving achieved in the last years have allowed to use this technology to solve many real-world applications, such as planning, formal verification and cryptography, among others. Interestingly, these industrial SAT problems are commonly believed to be easier than classical random SAT formulas, but estimating their actual hardness is still a very challenging question, which in some cases even requires to solve them. In this context, realistic pseudo-industrial random SAT generators have emerged with the aim of reproducing the main features of these application problems to better understand the success of those SAT solving techniques on them. In this work, we present a model to estimate the temperature of real-world SAT instances. This temperature represents the degree of distortion into the expected structure of the formula, from highly structured benchmarks (more similar to real-world SAT instances) to the complete absence of structure (observed in the classical random SAT model). Our solution is based on the popularity–similarity random model for SAT, which has been recently presented to reproduce two crucial features of application SAT benchmarks: scale-free and community structures. This model is able to control the hardness of the generated formula by introducing some randomizations in the expected structure. Using our regression model, we observe that the estimated temperature of the applications benchmarks used in the last SAT Competitions correlates to their hardness in most of the cases.Juan de la Cierva program, fellowship IJC2019-040489-I, funded by MCIN and AE

Roberto Arlt y el campo intelectual argentino de los años veinte y treinta

Abstract : Roberto Arlt and the Argentinian Intellectual Field of the 1920s and the 1930s. Taking as a basis Beatriz Sarlo and Carlos Altamirano\u27s analysis of the intellectual field (Literature and Society), inspired by Bourdieu\u27s work on the literary field, we are going to study the Argentinian intellectual field of the 1920s and the 1930s as well as the influence that Roberto Arlt had (or didn\u27t have) in this intellectual field. The writer\u27s short but prolific career —nowadays regarded as one of the greatest authors in the first half of the century— is, as a matter of fact, marked by his stormy relationship with most of the intellectual field in his days. When his misused Spanish and his use of lunfardo (slung of the slums of Buenos Aires) were censured, he, the son of immigrants, claimed his difference and vehemently criticized the ‘recognized’ authors, those who showered praise upon them and those who despised him

From language revalorisation to language revitalisation? :discourses of Maya language promotion in Yucatán

PhD ThesisAgainst the background of worldwide processes of language abandonment that are taking place at an unprecedented and rapid pace, in the last two decades language revitalisation has become an ever more prominent area of academic research. This thesis looks at the ideological underpinnings of Yucatec Maya language promotion in the Yucatán Peninsula of Mexico, based on the discourses of both official institutions and grassroots actors. After introducing the historical processes that have led to the present sociolinguistic minorisation of speakers of Maya in the Yucatán Peninsula, I analyse salient themes for language policy and planning pointed out by activists and institutions. Both official and grassroots discourses gathered in the field overwhelmingly revolve around the key concepts of revalorisation and rescate. These notions undergird the strategies that most participants consider as necessary for Maya language promotion, namely, the drafting of specific language legislation; the use of Maya in the education system; and an emphasis on the development of literacy in Maya. While policies in these areas may have a positive impact on raising the status and public profile of Maya and may lead to its legitimation, I argue that they present considerable limitations for actual revitalisation, which I believe should be part of a wider sociopolitical movement coming from the grassroots. On the one hand, vertical language policies that emanate from official institutions, the school being a prominent one, have been central in the cultural and linguistic assimilation to Spanish of indigenous peoples in Mexico. On the other hand, institutional policies that replicate the essentialist tenets of hegemonic languages on minorised languages, such as standardisation, actually devalue plurilingual and mixed practices on the ground and raise the issue of purism, which in the case of Yucatán may be contributing to language shift to Spanish and hindering the revitalisation process. Seen as an alternative and complementary project that comes above all from the ground up, I maintain that grassroots language promotion beyond institutional settings and control is effectively working towards the revitalisation of Maya. Along these lines, the use of this language in social media and modern music genres by youths, as part of their expanding communicative repertoires and heteroglossic practices on the ground, is opening up promising spaces for its maintenance and reproduction.Institut Ramon Llull and the School of Modern Languages at Newcastle University for offering me the possibility to teach Catalan in the North East while undertaking a doctoral degree. I would also like to thank the support of the Newcastle University Santander International Exchange Programme for fieldwork in Mexico