Locating leak detecting sensors in a water distribution network by solving prize-collecting Steiner arborescence problems

We consider the problem of optimizing a novel acoustic leakage detection system for urban water distribution networks. The system is composed of a number of detectors and transponders to be placed in a choice of hydrants such as to provide a desired coverage under given budget restrictions. The problem is modeled as a particular Prize-Collecting Steiner Arborescence Problem. We present a branch-and-cut-and-bound approach taking advantage of the special structure at hand which performs well when compared to other approaches. Furthermore, using a suitable stopping criterion, we obtain approximations of provably excellent quality (in most cases actually optimal solutions). The test bed includes the real water distribution network from the Lausanne region, as well as carefully randomly generated realistic instance

On non-rank facets of the stable set polytope of claw-free graphs and circulant graphs

We deal with non-rank facets of the stable set polytope of claw-free graphs. We extend results of Giles and Trotter [7] by (i) showing that for any nonnegative integer a there exists a circulant graph whose stable set polytope has a facet-inducing inequality with (a,a+1)-valued coefficients (rank facets have only coefficients 0, 1), and (ii) providing new facets of the stable set polytope with up to five different non-zero coefficients for claw-free graphs. We prove that coefficients have to be consecutive in any facet with exactly two different non-zero coefficients (assuming they are relatively prime). Last but not least, we present a complete description of the stable set polytope for graphs with stability number 2, already observed by Cook [3] and Shepherd [18

A generalization of distinct element method to tridimensional particles with complex shapes

The distinct element method was originally designed to handle spherical particles. Here, this method is generalized to a wider range of particle shapes called spherosimplices. A contact detection method is given as well which uses weighted Delaunay triangulations to detect contacts occurring in a population of particles with such shapes. Finally, a set of numerical experiments is performed indicating that the overall contact detection complexity is linear in the number of particles

Locating leak detecting sensors in a water distribution network by solving prize-collecting Steiner arborescence problems

We consider the problem of optimizing a novel acoustic leakage detection system for urban water distribution networks. The system is composed of a number of detectors and transponders to be placed in a choice of hydrants such as to provide a desired coverage under given budget restrictions. The problem is modeled as a particular Prize-Collecting Steiner Arborescence Problem. We present a branch-and-cut-and-bound approach taking advantage of the special structure at hand which performs well when compared to other approaches. Furthermore, using a suitable stopping criterion, we obtain approximations of provably excellent quality (in most cases actually optimal solutions). The test bed includes the real water distribution network from the Lausanne region, as well as carefully randomly generated realistic instances

Computational Analysis of Mesh Simplification Using Global Error

Meshes with (recursive) subdivision connectivity, such as subdivision surfaces, are increasingly popular in computer graphics. They present several advantages over their Delaunay-type based counterparts, e.g., Triangulated Irregular Networks (TINs), such as efficient processing, compact storage and numerical robustness. A mesh having subdivision connectivity can be described using a tree structure and recent work exploits this inherent hierarchy in applications such as progressive terrain visualization, surface compression and transmission. We propose a hierarchical, fine to coarse (i.e., using vertex decimation) algorithm to reduce the number of vertices in meshes whose connectivity is based on quadrilateral quadrisection (e.g., subdivision surfaces obtained from Catmull–Clark or 4-8 subdivision rules). Our method is derived from optimal tree pruning algorithms used in modeling of adaptive quantizers for compression. The main advantage of our method is that it allows control of the global error of the approximation, whereas previous methods are based on local error heuristics only. We present a set of operations allowing the use of global error and use them to build an O(nlogn) simplification algorithm transforming an input mesh of n vertices into a multiresolution hierarchy. Note that a single approximation having k<n vertices is obtained in linear running time. We show that, without using these operations, mesh simplification using global error has O(n2) computational complexity in the RAM model. Our approach uses a generalized vertex decimation method which allows for choosing the optimal vertex in the rate-distortion sense. Additionally, our algorithm can also be applied to other types of subdivision connectivity such as triangular quadrisection, e.g., obtained from Loop subdivision

QOBJ modeling A new approach in discrete event simulation

This paper deals with a new discrete event simulation modeling concept, calledqobj, which comes from two well- known paradigms:objects andqueuing networks. The first provides important conceptual tools for model organization, while the second one allows for nice visualization of models' internal state and processes. Thanks to the integration of these two paradigms, theqobj concept allows the suppression of several dichotomies characterizing current simulation modeling approaches. For instance,qobj allows the description of system elements which are both mobile and able to do processing, and allows the dynamic instantiation of static and mobile elements during simulation. The design of lift group models for an industrial project illustrates the main features of theqobj concept