Cèsar Fernández

Sensor networks and distributed CSP: communication, computation and complexity

We introduce SensorDCSP, a naturally distributed benchmark based on a real-world application that arises in the context of networked distributed systems. In order to study the performance of Distributed CSP (DisCSP) algorithms in a truly distributed setting, we use a discrete-event network simulator, which allows us to model the impact of different network traffic conditions on the performance of the algorithms. We consider two complete DisCSP algorithms: asynchronous backtracking (ABT) and asynchronous weak commitment search (AWC), and perform performance comparison for these algorithms on both satisfiable and unsatisfiable instances of SensorDCSP. We found that random delays (due to network traffic or in some cases actively introduced by the agents) combined with a dynamic decentralized restart strategy can improve the performance of DisCSP algorithms. In addition, we introduce GSensorDCSP, a plain-embedded version of SensorDCSP that is closely related to various real-life dynamic tracking systems. We perform both analytical and empirical study of this benchmark domain. In particular, this benchmark allows us to study the attractiveness of solution repairing for solving a sequence of DisCSPs that represent the dynamic tracking of a set of moving objects.

On the Complexity of Distributed Self-Configuration in Wireless Networks

We consider three distributed configuration tasks that arise in the setup and operation of multi-hop wireless networks: partition into coordinating cliques, Hamiltonian cycle formation and conflict-free channel allocation. We show that the probabilities of accomplishing these tasks undergo zero-one phase transitions with respect to the transmission range of individual nodes. We model these tasks as distributed constraint satisfaction problems (DCSPs) and show that, even though they are NP-hard in general, these problems can be solved efficiently on average when the network is operated sufficiently far from the transition region. Phase transition analysis is shown to be a useful mechanism for quantifying the critical range of energy and bandwidth resources needed for the scalable performance of self-configuring wireless networks.

Capturing Structure with Satisfiability

We present Regular-SAT, an extension of Boolean Satisfiability basedon a class of many-valuedCNF formulas. Regular-SAT shares many properties with Boolean SAT, which allows us to generalize some of the best known SAT results and apply them to Regular-SAT. In addition, Regular-SAT has a number of advantages over Boolean SAT. Most importantly, it produces more compact encodings that capture problem structure more naturally. Furthermore, its simplicity allows us to develop Regular-SAT solvers that are competitive with SAT and CSP procedures. We present a detailed performance analysis of Regular-SAT on several benchmark domains. These results show a clear computational advantage of using a Regular-SAT approach over a pure Boolean SAT or CSP approach, at least on the domains under consideration. We therefore believe that an approach basedon Regular-SAT provides a compelling intermediate approach between SAT and CSPs, bringing together some of the best features of each paradigm.

Monte carlo localization using SIFT features

The ability of finding its situation in a given environment is crucial for an autonomous agent. While navigating through a space, a mobile robot must be capable of finding its location in a map of the environment (i.e. its pose ), otherwise, the robot will not be able to complete its task. This problem becomes specially challenging if the robot does not possess any external measure of its global position. Typically, dead-reckoning systems do fail in the estimation of robots pose when working for long periods of time. In this paper we present a localization method based on the Monte Carlo algorithm. During the last decade this method has been extensively tested in the field of mobile Robotics, proving to be both robust and efficient. On the other hand, our approach takes advantage from the use of a vision sensor. In particular, we have chosen to use SIFT features as visual landmarks finding them suitable for the global localization of a mobile robot. We have succesfully tested our approach in a B21r mobile robot, achieving to globally localize the robot in few iterations. The technique is suitable for office-like environments and behaves correctly in the presence of people and moving objects.

Face recognition using multiple interest point detectors and SIFT descriptors

The use of interest point detectors and SIFT descriptors for face recognition is studied in this paper. There are two main novelties with respect to previous approaches using SIFT features. First, the use of two scale-invariant interest point detectors (namely, Harris-Laplace and difference of Gaussians) which are combined in order to detect both corner-like structures and blob-like structures in face images. Second, the distance measure used, which takes into account both the number of matching points found between two images (according to their SIFT descriptors) and the coherence of these matches in terms of scales, orientations and spacial configuration. The results obtained with our model-based algorithm are compared with those of a classic appearance-based face recognition method (PCA) over two different face databases: the well-known AT&T database and a face database created at our university.

Use of QR and EAN-13 codes by older patients taking multiple medications for a safer use of medication.

BACKGROUND Older persons following a prolonged complex drug regimen often make mistakes when taking their medication. Currently, the widespread use of tablets and smartphones has encouraged the development of applications to support self-management of medication. OBJECTIVE The aim of this study was to design, develop and assess an app that transforms medication-associated ean-13 (barcodes) and Quick Response codes (QR) into verbal instructions, to enable safer use of medication by the elderly patients taking multiple medications. METHODS Meetings were held in which participated a total of 61 patients. RESULTS The results showed that patients appreciated the application and found it useful for safer use of medicines. CONCLUSIONS The study results support the use of such technology to increase patient safety taking multiple medications safety.

Remote Control Laboratory Using Matlab and Simulink

In this paper, a teaching application for remote real-time execution of physical process controllers is presented. This application has been developed using the platform Matlab/Simulink. The motivation of this work is based on the little availability of real physical systems or laboratories to perform the experiments in control courses. In this way, control lab assignments with various physical processes present in the remote laboratories can be performed. Also, some examples that show the validity and applicability of the presented architecture are introduced.

Edge Matching Puzzles as Hard SAT/CSP Benchmarks

Recently, edge matching puzzles, an NP-complete problem, have received, thanks to money-prized contests, considerable attention from wide audiences. This paper studies edge matching puzzles focusing on providing generation models of problem instances of variable hardness and on its resolution through the application of SAT and CSP techniques. From the generation side, we also identify the phase transition phenomena for each model. As solving methods, we employ both; SAT solvers through the translation to a SAT formula, and two ad-hoc CSP solvers we have developed, with different levels of consistency, employing generic and specialized heuristics. Finally, we conducted an extensive experimental investigation to identify the hardest generation models and the best performing solving techniques.

Non existence of some mixed Moore graphs of diameter 2 using SAT

Mixed graphs with maximum number of vertices regarding to a given maximum degree and given diameter are known as mixed Moore graphs. In this paper we model the problem of the existence of mixed Moore graphs of diameter 2 through the Boolean satisfiability problem. As a consequence, we prove the non existence of mixed Moore graphs of order 40, 54 and 84.

Optimizing Energy Consumption in Automated Vacuum Waste Collection Systems

Automated vacuum waste collection (AVWC) uses air suction on a closed network of underground pipes to transport waste from the drop off points scattered throughout the city to a central collection point, reducing greenhouse gas emissions and the inconveniences of conventional methods (odors, noise). Since a significant part of the cost of operating AVWC systems is energy consumption, we have started a project, together with a company that builds and installs such systems, with the aim of applying constraint programming technology to schedule the daily emptying sequences of the drop off points in such a way that energy consumption is minimized. In this paper we describe how the problem of deciding the drop off points that should be emptied at a given time can be modeled as a constraint integer programming (CIP) problem. Moreover, we report on experiments using real data from AVWC systems installed in different cities that provide empirical evidence that CIP offers a suitable technology for reducing energy consumption in AVWC.