On Optimization Modulo Theories, MaxSMT and Sorting Networks

Optimization Modulo Theories (OMT) is an extension of SMT which allows for finding models that optimize given objectives. (Partial weighted) MaxSMT --or equivalently OMT with Pseudo-Boolean objective functions, OMT+PB-- is a very-relevant strict subcase of OMT. We classify existing approaches for MaxSMT or OMT+PB in two groups: MaxSAT-based approaches exploit the efficiency of state-of-the-art MAXSAT solvers, but they are specific-purpose and not always applicable; OMT-based approaches are general-purpose, but they suffer from intrinsic inefficiencies on MaxSMT/OMT+PB problems. We identify a major source of such inefficiencies, and we address it by enhancing OMT by means of bidirectional sorting networks. We implemented this idea on top of the OptiMathSAT OMT solver. We run an extensive empirical evaluation on a variety of problems, comparing MaxSAT-based and OMT-based techniques, with and without sorting networks, implemented on top of OptiMathSAT and {\nu}Z. The results support the effectiveness of this idea, and provide interesting insights about the different approaches.Comment: 17 pages, submitted at Tacas 1

Time representation in reinforcement learning models of the basal ganglia

Reinforcement learning (RL) models have been influential in understanding many aspects of basal ganglia function, from reward prediction to action selection. Time plays an important role in these models, but there is still no theoretical consensus about what kind of time representation is used by the basal ganglia. We review several theoretical accounts and their supporting evidence. We then discuss the relationship between RL models and the timing mechanisms that have been attributed to the basal ganglia. We hypothesize that a single computational system may underlie both RL and interval timing—the perception of duration in the range of seconds to hours. This hypothesis, which extends earlier models by incorporating a time-sensitive action selection mechanism, may have important implications for understanding disorders like Parkinson's disease in which both decision making and timing are impaired

A practical approach to communicating benefit-risk decisions of medicines to stakeholders.

© 2015 Leong, Walker and Salek. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.Purpose: The importance of a framework for a systematic structured assessment of the benefits and risks has been established, but in addition, it is necessary that the benefit-risk decisions and the processes to derive those decisions are documented and communicated to various stakeholders for accountability. Hence there is now a need to find appropriate tools to enhance communication between regulators and other stakeholders, in a manner that would uphold transparency, consistency and standards. Methods: A retrospective, non-comparative study was conducted to determine the applicability and practicality of a summary template in documenting benefit-risk assessment and communicating benefit-risk balance and conclusions for reviewers to other stakeholders. The benefit-risk (BR) Summary Template and its User Manual was evaluated by 12 reviewers within a regulatory agency in Singapore, the Health Sciences Authority (HSA). Results: The BR Summary Template was found to be adequate in documenting benefits, risks, relevant summaries and conclusions, while the User Manual was useful in guiding the reviewer in completing the template. The BR Summary Template was also considered a useful tool for communicating benefit-risk decisions to a variety of stakeholders. Conclusions: The use of a template may be of value for the communicating benefit-risk assessment of medicines to stakeholders.Peer reviewedFinal Published versio