Improvements and comparison of heuristics for solving the uncapacitated multisource Weber problem

Copyright @ 2000 INFORMSThe multisource Weber problem is to locate simultaneously m facilities in the Euclidean plane to minimize the total transportation cost for satisfying the demand of n fixed users, each supplied from its closest facility. Many heuristics have been proposed for this problem, as well as a few exact algorithms. Heuristics are needed to solve quickly large problems and to provide good initial solutions for exact algorithms. We compare various heuristics, i.e., alternative location-allocation (Cooper 1964), projection (Bongartz et al. 1994), Tabu search (Brimberg and Mladenovic 1996a), p-Median plus Weber (Hansen ct al. 1996), Genetic search and several versions of Variable Neighbourhood search. Based on empirical tests that are reported, it is found that most traditional and some recent heuristics give poor results when the number of facilities to locate is large and that Variable Neighbourhood search gives consistently best results, on average, in moderate computing time.This study was supported by the Department of National Defence (Canada) Academic Research; Office of Naval Research Grant N00014-92-J-1194, Natural Sciences and Engineering Research Council of Canada Grant GPO 105574 and Fonds pour la Formation des Chercheurs et l’Aide a la Recherche Grant 32EQ 1048; and by an International Postdoctoral Fellowship of the Natural Sciences and Engineering Research Council of Canada, Grant OGPOO 39682

Phase transformation yield surface of anisotropic shape memory alloys

International audienceTwo theoretical investigations, i.e. a phenomenological macroscopic model and a "micro-macro" model are developed for modelling the experimental surfaces of initiation of phase transformation in shape memory alloys. A possible initial anisotropy of the materials is taken into account

Pilot, Rollout and Monte Carlo Tree Search Methods for Job Shop Scheduling

Greedy heuristics may be attuned by looking ahead for each possible choice, in an approach called the rollout or Pilot method. These methods may be seen as meta-heuristics that can enhance (any) heuristic solution, by repetitively modifying a master solution: similarly to what is done in game tree search, better choices are identified using lookahead, based on solutions obtained by repeatedly using a greedy heuristic. This paper first illustrates how the Pilot method improves upon some simple well known dispatch heuristics for the job-shop scheduling problem. The Pilot method is then shown to be a special case of the more recent Monte Carlo Tree Search (MCTS) methods: Unlike the Pilot method, MCTS methods use random completion of partial solutions to identify promising branches of the tree. The Pilot method and a simple version of MCTS, using the $\varepsilon$-greedy exploration paradigms, are then compared within the same framework, consisting of 300 scheduling problems of varying sizes with fixed-budget of rollouts. Results demonstrate that MCTS reaches better or same results as the Pilot methods in this context.Comment: Learning and Intelligent OptimizatioN (LION'6) 7219 (2012

Heuristics in permutation GOMEA for solving the permutation flowshop scheduling problem

The recently introduced permutation Gene-pool Optimal Mixing Evolutionary Algorithm (GOMEA) has shown to be an effective Model Based Evolutionary Algorithm (MBEA) for permutation problems. So far, permutation GOMEA has only been used in the context of Black-Box Optimization (BBO). This paper first shows that permutation GOMEA can be improved by incorporating a constructive heuristic to seed the initial population. Secondly, the paper shows that hybridizing with job swapping neighborhood search does not lead to consistent improvement. The seeded permutation GOMEA is compared to a state-of-the-art algorithm (VNS4) for solving the Permutation Flowshop Scheduling Problem (PFSP). Both unstructured and structured instances are used in the benchmarks. The results show that permutation GOMEA often outperforms the VNS4 algorithm for the PFSP with the total flowtime criterion

Iterated maps for clarinet-like systems

The dynamical equations of clarinet-like systems are known to be reducible to a non-linear iterated map within reasonable approximations. This leads to time oscillations that are represented by square signals, analogous to the Raman regime for string instruments. In this article, we study in more detail the properties of the corresponding non-linear iterations, with emphasis on the geometrical constructions that can be used to classify the various solutions (for instance with or without reed beating) as well as on the periodicity windows that occur within the chaotic region. In particular, we find a regime where period tripling occurs and examine the conditions for intermittency. We also show that, while the direct observation of the iteration function does not reveal much on the oscillation regime of the instrument, the graph of the high order iterates directly gives visible information on the oscillation regime (characterization of the number of period doubligs, chaotic behaviour, etc.)

A Parallel Tabu Search Algorithm for Optimizing Multiobjective VLSI Placement

Abstract. In this paper, we present a parallel tabu search (TS) algorithm for efficient optimization of a constrained multiobjective VLSI standard cell placement problem. The primary purpose is to accelerate TS algorithm to reach near optimal placement solutions for large circuits. The proposed technique employs a candidate list partitioning strategy based on distribution of mutually disjoint set of moves among the slave processes. The implementation is carried out on a dedicated cluster of workstations. Experimental results using ISCAS-85/89 benchmark circuits illustrating quality and speedup trends are presented. A comparison of the obtained results is made with the results of a parallel genetic algorithm (GA) implementation

Astrochemical models of interstellar ices: History matters

Ice is ubiquitous in the interstellar medium. We model the formation of the main constituents of interstellar ices, including H2O, CO2 , CO, and CH3 OH. We strive to understand what physical or chemical parameters influence the final composition of the ice and how they benchmark to what has already been observed, with the aim of applying these models to the preparation and analysis of JWST observations. We used the Nautilus gas-grain model, which computes the gas and ice composition as a function of time for a set of physical conditions, starting from an initial gas phase composition. All important processes (gas-phase reactions, gas-grain interactions, and grain surface processes) are included and solved with the rate equation approximation. We first ran an astrochemical code for fixed conditions of temperature and density mapped in the cold core L429-C to benchmark the chemistry. One key parameter was revealed to be the dust temperature. When the dust temperature is higher than 12 K, CO2 will form efficiently at the expense of H2O, while at temperatures below 12 K, it will not form. Whatever hypothesis we assumed for the chemistry (within realistic conditions), the static simulations failed to reproduce the observed trends of interstellar ices in our target core. In a second step, we simulated the chemical evolution of parcels of gas undergoing different physical and chemical situations throughout the molecular cloud evolution and starting a few 1e7 yr prior to the core formation (dynamical simulations). Our dynamical simulations satisfactorily reproduce the main trends already observed for interstellar ices. Moreover, we predict that the apparent constant ratio of CO2/H2O observed to date is probably not true for regions of low AV , and that the history of the evolution of clouds plays an essential role, even prior to their formation.Comment: Accepted for publication in A&

Perturbation strength and the global structure of qap fitness landscapes

We study the effect of increasing the perturbation strength on the global structure of QAP fitness landscapes induced by Iterated Local Search (ILS). The global structure is captured with Local Optima Networks. Our analysis concentrates on the number, characteristics and distribution of funnels in the landscape, and how they change with increasing perturbation strengths. Well-known QAP instance types are considered. Our results confirm the multi-funnel structure of QAP fitness landscapes and clearly explain, visually and quantitatively, why ILS with large perturbation strengths produces better results. Moreover, we found striking differences between randomly generated and real-world instances, which warns about using synthetic benchmarks for (manual or automatic) algorithm design and tuning

Immunogenicity and safety of yellow fever vaccination for 102 HIV-infected patients

BACKGROUND: Yellow fever vaccine (17DV) has been investigated incompletely in human immunodeficiency virus (HIV)-infected patients, and adequate immunogenicity and safety are of concern in this population. METHODS: In the Swiss HIV Cohort Study, we identified 102 patients who received 17DV while they were HIV infected. We analyzed neutralization titers (NTs) after 17DV administration using the plaque reduction neutralization test. NTs of 1:>or=10 were defined as reactive, and those of 1:<10 were defined as nonreactive, which was considered to be nonprotective. The results were compared with data for HIV-uninfected individuals. Serious adverse events were defined as hospitalization or death within 6 weeks after receipt of 17DV. RESULTS: At the time of 17DV administration, the median CD4 cell count was 537 cells/mm(3) (range, 11-1730 cells/mm(3)), and the HIV RNA level was undetectable in 41 of 102 HIV-infected patients. During the first year after vaccination, fewer HIV-infected patients (65 [83%] of 78; P = .01) than HIV-uninfected patients revealed reactive NTs, and their NTs were significantly lower (P < .001) than in HIV-uninfected individuals. Eleven patients with initially reactive NTs lost these reactive NTs <or= 5 years after vaccination. Higher NTs during the first year after vaccination were associated with undetectable HIV RNA levels, increasing CD4 cell count, and female sex. We found no serious adverse events after 17DV administration among HIV-infected patients. CONCLUSION: Compared with HIV-uninfected individuals, HIV-infected patients respond to 17DV with lower reactive NTs, more often demonstrate nonprotective NTs, and may experience a more rapid decline in NTs during follow-up. Vaccination with 17DV appears to be safe in HIV-infected individuals who have high CD4 cell counts, although rate of serious adverse events of up to 3% cannot be exclude