Automated Benchmarking of Incremental SAT and QBF Solvers

Incremental SAT and QBF solving potentially yields improvements when sequences of related formulas are solved. An incremental application is usually tailored towards some specific solver and decomposes a problem into incremental solver calls. This hinders the independent comparison of different solvers, particularly when the application program is not available. As a remedy, we present an approach to automated benchmarking of incremental SAT and QBF solvers. Given a collection of formulas in (Q)DIMACS format generated incrementally by an application program, our approach automatically translates the formulas into instructions to import and solve a formula by an incremental SAT/QBF solver. The result of the translation is a program which replays the incremental solver calls and thus allows to evaluate incremental solvers independently from the application program. We illustrate our approach by different hardware verification problems for SAT and QBF solvers.Comment: camera-ready version (8 pages + 2 pages appendix), to appear in the proceedings of the 20th International Conference on Logic for Programming, Artificial Intelligence and Reasoning (LPAR), LNCS, Springer, 201

DEFORMACIÓN TECTÓNICA RECIENTE EN LOS PIE DE MONTES DE LAS CORDILLERAS CENTRAL Y OCCIDENTAL, VALLE DEL CAUCA, COLOMBIA

La cuenca intramontana del río Cauca, por situarse cerca del margen activo en el occidente colombiano, es una de las regiones claves para comprender la evolución estructural y la actividad sísmica reciente de los Andes más occidentales en Colombia. El descubrimiento de rasgos de actividad neotectónica en esta cuenca, entre Cali y Cartago, y la aplicación de análisis tectónico y radiométrico condujo a la caracterización de tres zonas con rasgos morfoestructurales distintivos: 1) Pie de monte de la Cordillera Central. Presenta fallas normales coetáneas con depósitos Miocenos que fueron reactivadas como fallas inversas durante el Cuaternario, y retrocabalgamientos que sugieren la existencia de una cuña subcrítica. Análisis radiométricos indican la naturaleza episódica de la actividad neotectónica. 2) Pie de monte de la Cordillera Occidental. Dominan fallas con componentes horizontales sobre los de inclinación. 3) Llanura aluvial del río Cauca. Es común el fallamiento distensivo en depósitos lacustres y fluviales recientes. Las estructuras sedimentarias relacionadas con las fallas sugieren que la mayor parte de ellas fueron producidas por licuación del substrato fino durante sacudidas sísmicas. El gradiente topográfico, a lo largo del río Cauca no es uniforme, muestra una mayor pendiente y mayor grado de sinuosidad frente a las escamas de cabalgamiento de la Saliente de Buga. Los resultados de este trabajo se discuten y comparan con la información vigente y se hace una propuesta de modelo estructural para este sector del occidente colombiano.  Palabras clave: Anticlinal activo, cinturón de cabalgamiento, fallamiento ciego activo, licuación, sinuosidad y gradiente río Cauca.    The intermountain basin of the Cauca River, located close to the active margin in western Colombia, is one of the keys to understand the evolution and recent seismic activity in the westernmost Andes in Colombia. The discovery of evidences of neotectonic activity in this basin, between Cali and Cartago, and the application of tectonic and radiometric analysis led to the characterization of three zones with distinctive morpho-structural expressions: 1) Foothills of the Cordillera Central. It shows contemporary normal faulting with Miocene deposits that were reactivated as reverse faults during Quaternary, and backthrusts indicating the existence of a subcritical wedge. Radiometric analysis indicate the episodic nature of the neotectonic activity. 2) Foothills of the Cordillera Occidental. The horizontal component of faulting is predominant over the dip-slip one. 3) Floodplain of the Cauca river. Extensional faulting is common on recent fluvial and lacustrine deposits. Sedimentary structures related to faulting suggest that most of them were produced by liquefaction of the substrate during seismic shaking. The topographic gradient, along the Cauca River is not uniform, it shows a higher slope and greater sinuosity in front of the thrust sheets of the Buga Salient. The results of this work are discussed and compared with existing information and a structural model is provided for this area of western Colombia. Keywords: Active anticline, fold and thrust belt, active blind faulting, liquefaction, Cauca river gradient and sinuosity

DEFORMACIÓN TECTÓNICA RECIENTE EN LOS PIE DE MONTES DE LAS CORDILLERAS CENTRAL Y OCCIDENTAL, VALLE DEL CAUCA, COLOMBIA

La cuenca intramontana del río Cauca, por situarse cerca del margen activo en el occidente colombiano, es una de las regiones claves para comprender la evolución estructural y la actividad sísmica reciente de los Andes más occidentales en Colombia. El descubrimiento de rasgos de actividad neotectónica en esta cuenca, entre Cali y Cartago, y la aplicación de análisis tectónico y radiométrico condujo a la caracterización de tres zonas con rasgos morfoestructurales distintivos: 1) Pie de monte de la Cordillera Central. Presenta fallas normales coetáneas con depósitos Miocenos que fueron reactivadas como fallas inversas durante el Cuaternario, y retrocabalgamientos que sugieren la existencia de una cuña subcrítica. Análisis radiométricos indican la naturaleza episódica de la actividad neotectónica. 2) Pie de monte de la Cordillera Occidental. Dominan fallas con componentes horizontales sobre los de inclinación. 3) Llanura aluvial del río Cauca. Es común el fallamiento distensivo en depósitos lacustres y fluviales recientes. Las estructuras sedimentarias relacionadas con las fallas sugieren que la mayor parte de ellas fueron producidas por licuación del substrato fino durante sacudidas sísmicas. El gradiente topográfico, a lo largo del río Cauca no es uniforme, muestra una mayor pendiente y mayor grado de sinuosidad frente a las escamas de cabalgamiento de la Saliente de Buga. Los resultados de este trabajo se discuten y comparan con la información vigente y se hace una propuesta de modelo estructural para este sector del occidente colombiano.  Palabras clave: Anticlinal activo, cinturón de cabalgamiento, fallamiento ciego activo, licuación, sinuosidad y gradiente río Cauca.    The intermountain basin of the Cauca River, located close to the active margin in western Colombia, is one of the keys to understand the evolution and recent seismic activity in the westernmost Andes in Colombia. The discovery of evidences of neotectonic activity in this basin, between Cali and Cartago, and the application of tectonic and radiometric analysis led to the characterization of three zones with distinctive morpho-structural expressions: 1) Foothills of the Cordillera Central. It shows contemporary normal faulting with Miocene deposits that were reactivated as reverse faults during Quaternary, and backthrusts indicating the existence of a subcritical wedge. Radiometric analysis indicate the episodic nature of the neotectonic activity. 2) Foothills of the Cordillera Occidental. The horizontal component of faulting is predominant over the dip-slip one. 3) Floodplain of the Cauca river. Extensional faulting is common on recent fluvial and lacustrine deposits. Sedimentary structures related to faulting suggest that most of them were produced by liquefaction of the substrate during seismic shaking. The topographic gradient, along the Cauca River is not uniform, it shows a higher slope and greater sinuosity in front of the thrust sheets of the Buga Salient. The results of this work are discussed and compared with existing information and a structural model is provided for this area of western Colombia. Keywords: Active anticline, fold and thrust belt, active blind faulting, liquefaction, Cauca river gradient and sinuosity

Incrementally Computing Minimal Unsatisfiable Cores of QBFs via a Clause Group Solver API

We consider the incremental computation of minimal unsatisfiable cores (MUCs) of QBFs. To this end, we equipped our incremental QBF solver DepQBF with a novel API to allow for incremental solving based on clause groups. A clause group is a set of clauses which is incrementally added to or removed from a previously solved QBF. Our implementation of the novel API is related to incremental SAT solving based on selector variables and assumptions. However, the API entirely hides selector variables and assumptions from the user, which facilitates the integration of DepQBF in other tools. We present implementation details and, for the first time, report on experiments related to the computation of MUCs of QBFs using DepQBF's novel clause group API.Comment: (fixed typo), camera-ready version, 6-page tool paper, to appear in proceedings of SAT 2015, LNCS, Springe

Experimental Evaluation of Subgraph Isomorphism Solvers

International audienceSubgraph Isomorphism (SI) is an NP-complete problem which is at the heart of many structural pattern recognition tasks as it involves finding a copy of a pattern graph into a target graph. In the pattern recognition community, the most well-known SI solvers are VF2, VF3, and RI. SI is also widely studied in the constraint programming community, and many constraint-based SI solvers have been proposed since Ullman, such as LAD and Glasgow, for example. All these SI solvers can solve very quickly some large SI instances, that involve graphs with thousands of nodes. However, McCreesh et al. have recently shown how to randomly generate SI instances the hardness of which can be controlled and predicted, and they have built small instances which are computationally challenging for all solvers. They have also shown that some small instances, which are predicted to be easy and are easily solved by constraint-based solvers, appear to be challenging for VF2 and VF3. In this paper, we widen this study by considering a large test suite coming from eight benchmarks. We show that, as expected for an NP-complete problem, the solving time of an instance does not depend on its size, and that some small instances coming from real applications are not solved by any of the considered solvers. We also show that, if RI and VF3 can solve very quickly a large number of easy instances, for which Glasgow or LAD need more time, they fail at solving some other instances that are quickly solved by Glasgow or LAD, and they are clearly outperformed by Glasgow on hard instances. Finally, we show that we can easily combine solvers to take benefit of their complementarity

On Solving Word Equations Using SAT

We present Woorpje, a string solver for bounded word equations (i.e., equations where the length of each variable is upper bounded by a given integer). Our algorithm works by reformulating the satisfiability of bounded word equations as a reachability problem for nondeterministic finite automata, and then carefully encoding this as a propositional satisfiability problem, which we then solve using the well-known Glucose SAT-solver. This approach has the advantage of allowing for the natural inclusion of additional linear length constraints. Our solver obtains reliable and competitive results and, remarkably, discovered several cases where state-of-the-art solvers exhibit a faulty behaviour

Weight-Aware Core Extraction in SAT-Based MaxSAT Solving

Peer reviewe

On Tackling the Limits of Resolution in SAT Solving

The practical success of Boolean Satisfiability (SAT) solvers stems from the CDCL (Conflict-Driven Clause Learning) approach to SAT solving. However, from a propositional proof complexity perspective, CDCL is no more powerful than the resolution proof system, for which many hard examples exist. This paper proposes a new problem transformation, which enables reducing the decision problem for formulas in conjunctive normal form (CNF) to the problem of solving maximum satisfiability over Horn formulas. Given the new transformation, the paper proves a polynomial bound on the number of MaxSAT resolution steps for pigeonhole formulas. This result is in clear contrast with earlier results on the length of proofs of MaxSAT resolution for pigeonhole formulas. The paper also establishes the same polynomial bound in the case of modern core-guided MaxSAT solvers. Experimental results, obtained on CNF formulas known to be hard for CDCL SAT solvers, show that these can be efficiently solved with modern MaxSAT solvers

A SAT Approach to Clique-Width

Clique-width is a graph invariant that has been widely studied in combinatorics and computer science. However, computing the clique-width of a graph is an intricate problem, the exact clique-width is not known even for very small graphs. We present a new method for computing the clique-width of graphs based on an encoding to propositional satisfiability (SAT) which is then evaluated by a SAT solver. Our encoding is based on a reformulation of clique-width in terms of partitions that utilizes an efficient encoding of cardinality constraints. Our SAT-based method is the first to discover the exact clique-width of various small graphs, including famous graphs from the literature as well as random graphs of various density. With our method we determined the smallest graphs that require a small pre-described clique-width.Comment: proofs in section 3 updated, results remain unchange

Genetic Relations Between the Aves Ridge and the Grenada Back-Arc Basin, East Caribbean Sea

The Grenada Basin separates the active Lesser Antilles Arc from the Aves Ridge, described as a Cretaceous‐Paleocene remnant of the “Great Arc of the Caribbean.” Although various tectonic models have been proposed for the opening of the Grenada Basin, the data on which they rely are insufficient to reach definitive conclusions. This study presents, a large set of deep‐penetrating multichannel seismic reflection data and dredge samples acquired during the GARANTI cruise in 2017. By combining them with published data including seismic reflection data, wide‐angle seismic data, well data and dredges, we refine the understanding of the basement structure, depositional history, tectonic deformation and vertical motions of the Grenada Basin and its margins as follows: (1) rifting occurred during the late Paleocene‐early Eocene in a NW‐SE direction and led to seafloor spreading during the middle Eocene; (2) this newly formed oceanic crust now extends across the eastern Grenada Basin between the latitude of Grenada and Martinique; (3) asymmetrical pre‐Miocene depocenters support the hypothesis that the southern Grenada Basin originally extended beneath the present‐day southern Lesser Antilles Arc and probably partly into the present‐day forearc before the late Oligocene‐Miocene rise of the Lesser Antilles Arc; and (4) the Aves Ridge has subsided along with the Grenada Basin since at least the middle Eocene, with a general subsidence slowdown or even an uplift during the late Oligocene, and a sharp acceleration on its southeastern flank during the late Miocene. Until this acceleration of subsidence, several bathymetric highs remained shallow enough to develop carbonate platforms