Discrete analogue computing with rotor-routers

Rotor-routing is a procedure for routing tokens through a network that can implement certain kinds of computation. These computations are inherently asynchronous (the order in which tokens are routed makes no difference) and distributed (information is spread throughout the system). It is also possible to efficiently check that a computation has been carried out correctly in less time than the computation itself required, provided one has a certificate that can itself be computed by the rotor-router network. Rotor-router networks can be viewed as both discrete analogues of continuous linear systems and deterministic analogues of stochastic processes.Comment: To appear in Chaos Special Focus Issue on Intrinsic and Designed Computatio

Camera-Based Distance Sensor

While working on a robotics project at the electrical contracting company for which we work, we discovered a gap in the electronic distance sensor market in terms of range, accuracy, precision, and cost. We designed and constructed a prototype for an electronic distance sensing component which utilizes a camera, laser, and image processor to measure distances. The laser is pointed at a surface and an image of the laser dot is captured. An image processing algorithm determines the pixel position of the dot in the image, and this position is compared to a lookup table of known values to determine the distance to the dot. In measuring our prototype’s performance, we found that it was capable of measuring distances up to 5 meters with greater than 90% accuracy. We also discuss some possible ways to improve the viability of the technology, including ways to improve the refresh rate as well as the reliability

Extending ACL2 with SMT Solvers

We present our extension of ACL2 with Satisfiability Modulo Theories (SMT) solvers using ACL2's trusted clause processor mechanism. We are particularly interested in the verification of physical systems including Analog and Mixed-Signal (AMS) designs. ACL2 offers strong induction abilities for reasoning about sequences and SMT complements deduction methods like ACL2 with fast nonlinear arithmetic solving procedures. While SAT solvers have been integrated into ACL2 in previous work, SMT methods raise new issues because of their support for a broader range of domains including real numbers and uninterpreted functions. This paper presents Smtlink, our clause processor for integrating SMT solvers into ACL2. We describe key design and implementation issues and describe our experience with its use.Comment: In Proceedings ACL2 2015, arXiv:1509.0552

Algorithms and Speech

One of the central questions in free speech jurisprudence is what activities the First Amendment encompasses. This Article considers that question in the context of an area of increasing importance – algorithm-based decisions. I begin by looking to broadly accepted legal sources, which for the First Amendment means primarily Supreme Court jurisprudence. That jurisprudence provides for very broad First Amendment coverage, and the Court has reinforced that breadth in recent cases. Under the Court’s jurisprudence the First Amendment (and the heightened scrutiny it entails) would apply to many algorithm-based decisions, specifically those entailing substantive communications. We could of course adopt a limiting conception of the First Amendment, but any nonarbitrary exclusion of algorithm-based decisions would require major changes in the Court’s jurisprudence. I believe that First Amendment coverage of algorithm-based decisions is too small a step to justify such changes. But insofar as we are concerned about the expansiveness of First Amendment coverage, we may want to limit it in two areas of genuine uncertainty: editorial decisions that are neither obvious nor communicated to the reader, and laws that single out speakers but do not regulate their speech. Even with those limitations, however, an enormous and growing amount of activity will be subject to heightened scrutiny absent a fundamental reorientation of First Amendment jurisprudence

Algorithms and Speech

One of the central questions in free speech jurisprudence is what activities the First Amendment encompasses. This Article considers that question in the context of an area of increasing importance – algorithm-based decisions. I begin by looking to broadly accepted legal sources, which for the First Amendment means primarily Supreme Court jurisprudence. That jurisprudence provides for very broad First Amendment coverage, and the Court has reinforced that breadth in recent cases. Under the Court’s jurisprudence the First Amendment (and the heightened scrutiny it entails) would apply to many algorithm-based decisions, specifically those entailing substantive communications. We could of course adopt a limiting conception of the First Amendment, but any nonarbitrary exclusion of algorithm-based decisions would require major changes in the Court’s jurisprudence. I believe that First Amendment coverage of algorithm-based decisions is too small a step to justify such changes. But insofar as we are concerned about the expansiveness of First Amendment coverage, we may want to limit it in two areas of genuine uncertainty: editorial decisions that are neither obvious nor communicated to the reader, and laws that single out speakers but do not regulate their speech. Even with those limitations, however, an enormous and growing amount of activity will be subject to heightened scrutiny absent a fundamental reorientation of First Amendment jurisprudence

The Myths of Macpherson

For a symposium marking the centenary of MacPherson v. Buick, we identify three common characterizations of Cardozo’s famous opinion that purport to explain its importance. Unfortunately, each of these characterizations turns out to be a myth. MacPherson is worthy of celebration, but not because it recognizes that negligence law’s duty of care is owed to the world, nor because it displays the promise of an instrumental, policy-oriented approach to adjudication, nor because it embraces a nascent form of strict products liability. These myths of MacPherson reflect deep misunderstandings of tort law, and of Cardozo’s distinctively pragmatic approach to adjudication. Ironically, although they have been largely fostered by progressives, the myths lend support to the cause of modern tort reform. By contrast, an accurate appreciation of MacPherson’s virtues permits an understanding of negligence, tort law, and common law adjudication that provides grounds for resisting regressive reforms