Cooperative Convex Optimization in Networked Systems: Augmented Lagrangian Algorithms with Directed Gossip Communication

We study distributed optimization in networked systems, where nodes cooperate to find the optimal quantity of common interest, x=x^\star. The objective function of the corresponding optimization problem is the sum of private (known only by a node,) convex, nodes' objectives and each node imposes a private convex constraint on the allowed values of x. We solve this problem for generic connected network topologies with asymmetric random link failures with a novel distributed, decentralized algorithm. We refer to this algorithm as AL-G (augmented Lagrangian gossiping,) and to its variants as AL-MG (augmented Lagrangian multi neighbor gossiping) and AL-BG (augmented Lagrangian broadcast gossiping.) The AL-G algorithm is based on the augmented Lagrangian dual function. Dual variables are updated by the standard method of multipliers, at a slow time scale. To update the primal variables, we propose a novel, Gauss-Seidel type, randomized algorithm, at a fast time scale. AL-G uses unidirectional gossip communication, only between immediate neighbors in the network and is resilient to random link failures. For networks with reliable communication (i.e., no failures,) the simplified, AL-BG (augmented Lagrangian broadcast gossiping) algorithm reduces communication, computation and data storage cost. We prove convergence for all proposed algorithms and demonstrate by simulations the effectiveness on two applications: l_1-regularized logistic regression for classification and cooperative spectrum sensing for cognitive radio networks.Comment: 28 pages, journal; revise

Improving the Efficiency of FP-LAPW Calculations

The full-potential linearized augmented-plane wave (FP-LAPW) method is well known to enable most accurate calculations of the electronic structure and magnetic properties of crystals and surfaces. The implementation of atomic forces has greatly increased it's applicability, but it is still generally believed that FP-LAPW calculations require substantial higher computational effort compared to the pseudopotential plane wave (PPW) based methods. In the present paper we analyse the FP-LAPW method from a computational point of view. Starting from an existing implementation (WIEN95 code), we identified the time consuming parts and show how some of them can be formulated more efficiently. In this context also the hardware architecture plays a crucial role. The remaining computational effort is mainly determined by the setup and diagonalization of the Hamiltonian matrix. For the latter, two different iterative schemes are compared. The speed-up gained by these optimizations is compared to the runtime of the ``original'' version of the code, and the PPW approach. We expect that the strategies described here, can also be used to speed up other computer codes, where similar tasks must be performed.Comment: 20 pages, 3 figures. Appears in Comp. Phys. Com. Other related publications can be found at http://www.rz-berlin.mpg.de/th/paper.htm

Development of PV powered consumer products using future scenarios

Given the high potential of PV technology to reduce the environmental impact of electricity use of consumer products, it would be worthwhile to advance the application of PV systems in mass produced products. To date this field of application has been explored only to a limited extent. For this reason the developers of consumer products, the industrial designers, might be unaware of the possibilities of product-integrated PV systems [1][2]. Their focus on the utility of consumer products might have an added value to existing R&D of PV technology which emphasizes on increased performance and decreased production cost. In the nearby future integration of both points of view might be important to better integrate PV cells in consumer products. Therefore, in this paper, we will assess industrial product design of integrated PV technology in the context of future scenarios. In our project about 25 product designers have conceptually designed products with integrated flexible PV cells within a future scenario. By observing the resulting cases we can evaluate how the design process was established in the framework of integrated technology design, the product phase model and future scenarios. The PV-powered products that will be evaluated are an electronic book, an information bracelet, a floating platform, sports garment and a robotic monitoring device. Each product is supported by visual materials such as renderings and an explanation of the design process based on scenarios

Real Exchange Rate Behavior Under Floating and Fixed Regimes

In this paper we examine the stability of the real exchange rate and the macroeconomic effects of alternative exchange-rate regimes, including currency union, on real exchange-rate behaviour. We focus on the Irish punt in order to exploit its diversity of experience over different nominal exchange rate regimes. We make both temporal and cross-country comparisons of real-exchange-rate stability for the Irish punt with sterling, the US dollar and the German mark. We reach two conclusions on the basis of our results. The first is that for Ireland, as for most other countries, purchasing power parity provides a reasonably good description of actual exchange rate behaviour over the long run. Our second principal conclusion concerns regime effects. Currency union appears to matter. The real exchange rates we analyse are unambiguously less variable under currency union than under alternative exchange-rate systems. Otherwise, however, we find no clear-cut differences in behaviour across regimes.Exchange Rates, purchasing power parity, exchange-rate regimes, currency union

MetaSpace II: Object and full-body tracking for interaction and navigation in social VR

MetaSpace II (MS2) is a social Virtual Reality (VR) system where multiple users can not only see and hear but also interact with each other, grasp and manipulate objects, walk around in space, and get tactile feedback. MS2 allows walking in physical space by tracking each user's skeleton in real-time and allows users to feel by employing passive haptics i.e., when users touch or manipulate an object in the virtual world, they simultaneously also touch or manipulate a corresponding object in the physical world. To enable these elements in VR, MS2 creates a correspondence in spatial layout and object placement by building the virtual world on top of a 3D scan of the real world. Through the association between the real and virtual world, users are able to walk freely while wearing a head-mounted device, avoid obstacles like walls and furniture, and interact with people and objects. Most current virtual reality (VR) environments are designed for a single user experience where interactions with virtual objects are mediated by hand-held input devices or hand gestures. Additionally, users are only shown a representation of their hands in VR floating in front of the camera as seen from a first person perspective. We believe, representing each user as a full-body avatar that is controlled by natural movements of the person in the real world (see Figure 1d), can greatly enhance believability and a user's sense immersion in VR.Comment: 10 pages, 9 figures. Video: http://living.media.mit.edu/projects/metaspace-ii

Explaining exchange rate behavior : an augmented version of the monetary approach

An abstract of this article is not available.Foreign exchange rates ; Monetary policy