Additive versus multiplicative clause weighting for SAT

This paper examines the relative performance of additive and multiplicative clause weighting schemes for propositional satisfiability testing. Starting with one of the most recently developed multiplicative algorithms (SAPS), an experimental study was constructed to isolate the effects of multiplicative in comparison to additive weighting, while controlling other key features of the two approaches, namely the use of random versus flat moves, deterministic versus probabilistic weight smoothing and multiple versus single inclusion of literals in the local search neighborhood. As a result of this investigation we developed a pure additive weighting scheme (PAWS) which can outperform multiplicative weighting on a range of difficult problems, while requiring considerably less effort in terms of parameter tuning. W

The Varying Roles of Morphosyntax in Memory and Sentence Processing: Retrieval and Encoding Interference in Brazilian Portuguese

Cue-based retrieval models have largely been adopted as a description of how linguistic content is retrieved from memory. Under this framework, a retrieval cue is projected at the site of a dependency and matched with its target using a parallel matching procedure (e.g., Van Dyke and Lewis, 2003). Although this is a highly efficient mechanism, retrieval difficulties occur when there are multiple items stored in memory that serve as potential matches for the retrieval cue(s), which is known as similarity-based interference (SBI). Several studies have demonstrated that a wide variety of linguistic information can generate SBI effects, but the theory of what serves as a retrieval cue is still relatively unknown (Van Dyke and Johns, 2012). Moreover, recent empirical evidence has proposed the similarity-based interference can arise from another source: the encoding mechanism (e.g., Villata et al., 2018). Three hypotheses are addressed regarding three potential retrieval mechanisms: (1) a retrieval mechanism that only relies on cues relevant to the dependency being resolved, (2) one that is sensitive to all of the features overlapping between a target and distractor(s), or (3) a mechanism that is primarily sensitive to relevant features but produces additive interference effects for irrelevant features. Moreover, a fourth hypothesis investigates if similarity-based interference also arises from the encoding mechanism. In an attempt to disentangle whether sentence processing disruptions occur as a result of retrieval mechanism (1) + encoding interference or due to one of the other mechanisms, 7 self-paced reading experiments were conducted on Brazilian Portuguese. In all of the studies, number was a relevant feature for the resolution of the grammatical dependency (subject-verb dependency in relative clauses or wh-remnant-correlate pairing in sluices) and gender features varied in their relevance. The rationale behind using these dependencies and features was to test whether syntactically relevant features produced stronger interference effects than irrelevant features and to propose why these results differed. Any findings that showed that irrelevant feature (gender) matches caused reading time slowdowns or decreased comprehension question accuracy before the retrieval site were interpreted as encoding interference.Although results vary across studies, the findings in this thesis provide the most support for a combination of retrieval (mechanism 1) and encoding interference. Although the other two retrieval mechanisms cannot be completely ruled out at this time, the evidence that gender produces earlier and weaker effects reminiscent of encoding interference and that number produced interference reflective of retrieval interference are novel

Taming a non-convex landscape with dynamical long-range order: memcomputing Ising benchmarks

Recent work on quantum annealing has emphasized the role of collective behavior in solving optimization problems. By enabling transitions of clusters of variables, such solvers are able to navigate their state space and locate solutions more efficiently despite having only local connections between elements. However, collective behavior is not exclusive to quantum annealers, and classical solvers that display collective dynamics should also possess an advantage in navigating a non-convex landscape. Here, we give evidence that a benchmark derived from quantum annealing studies is solvable in polynomial time using digital memcomputing machines, which utilize a collection of dynamical components with memory to represent the structure of the underlying optimization problem. To illustrate the role of memory and clarify the structure of these solvers we propose a simple model of these machines that demonstrates the emergence of long-range order. This model, when applied to finding the ground state of the Ising frustrated-loop benchmarks, undergoes a transient phase of avalanches which can span the entire lattice and demonstrates a connection between long-range behavior and their probability of success. These results establish the advantages of computational approaches based on collective dynamics of continuous dynamical systems

Respecting Relations: Memory Access and Antecedent Retrieval in Incremental Sentence Processing

This dissertation uses the processing of anaphoric relations to probe how linguistic information is encoded in and retrieved from memory during real-time sentence comprehension. More specifically, the dissertation attempts to resolve a tension between the demands of a linguistic processor implemented in a general-purpose cognitive architecture and the demands of abstract grammatical constraints that govern language use. The source of the tension is the role that abstract configurational relations (such as c-command, Reinhart 1983) play in constraining computations. Anaphoric dependencies are governed by formal grammatical constraints stated in terms of relations. For example, Binding Principle A (Chomsky 1981) requires that antecedents for local anaphors (like the English reciprocal each other) bear the c-command relation to those anaphors. In incremental sentence processing, antecedents of anaphors must be retrieved from memory. Recent research has motivated a model of processing that exploits a cue-based, associative retrieval process in content-addressable memory (e.g. Lewis, Vasishth & Van Dyke 2006) in which relations such as c-command are difficult to use as cues for retrieval. As such, the c-command constraints of formal grammars are predicted to be poorly implemented by the retrieval mechanism. I examine retrieval's sensitivity to three constraints on anaphoric dependencies: Principle A (via Hindi local reciprocal licensing), the Scope Constraint on bound-variable pronoun licensing (often stated as a c-command constraint, though see Barker 2012), and Crossover constraints on pronominal binding (Postal 1971, Wasow 1972). The data suggest that retrieval exhibits fidelity to the constraints: structurally inaccessible NPs that match an anaphoric element in morphological features do not interfere with the retrieval of an antecedent in most cases considered. In spite of this alignment, I argue that retrieval's apparent sensitivity to c-command constraints need not motivate a memory access procedure that makes direct reference to c-command relations. Instead, proxy features and general parsing operations conspire to mimic the extension of a system that respects c-command constraints. These strategies provide a robust approximation of grammatical performance while remaining within the confines of a independently- motivated general-purpose cognitive architecture

A methodology for the interpretation of ground conditions from borehole information.

Geotechnical design requires the interpretation of the information obtained from a site investigation. One aspect of the interpretation is the identification of the ground conditions across the site, based on observations at discrete points, such as boreholes. If a computer system is to assist in this process it must be able to compare soils observed at two or more locations, in order to identify whether the soils observed belong to the same horizon. A methodology has been developed whereby the similarity of two soils can be calculated, based on engineering soil descriptions. The qualitative terms are converted into quantitative representations from which a Similarity Number can be derived. Individual Similarity Numbers can be calculated with respect to soil type, consistency, structure and colour. These are normalised to give values between 0 and 100 (with 100 indicating identical features) and combined using appropriate weighting factors to give an Overall Similarity Number which represents a comparison based on these features. Using die quantitative representation of the soil descriptions, a preliminary assessment of the ground conditions can be made. The correlation of the borehole information is approached at two levels. At the site-wide level, an attempt is made to identify marker beds, that is soil layers which 'stand out' from the general ground conditions. A search for possible marker beds is first made at each borehole. The search is then extended to pairs of boreholes and further, the continuity of marker beds is established inside triangles which are formed having the boreholes as vertices. Where continuous layers are observed within triangles, the dip angle and dip orientation are calculated, to form the geometrical parameters on which preliminary conclusions are based. Compatibility (or not) of these parameters between neighbouring triangles is the key factor for assessing continuity of the marker beds. Finally, the detailed ground conditions are examined on a borehole-to-borehole level. At this level, a set of hypotheses about the ground conditions is constructed by looking at pairs of adjacent boreholes. Hence, a set of hypotheses is produced, even for areas for which the site-wide level approach is unable to establish trends