David Soler

A new genetic algorithm for the asymmetric traveling salesman problem

Highlights? This paper presents a genetic algorithm for solving the asymmetric traveling salesman problem. ? Experimental results demonstrate that the proposed GA outperforms state-of-the-art heuristic algorithms. ? Effective crossover operator for the ATSP is designed. ? We provide useful insights for designing effective GAs. ? We create a new set of benchmarks for the ATSP. The asymmetric traveling salesman problem (ATSP) is one of the most important combinatorial optimization problems. It allows us to solve, either directly or through a transformation, many real-world problems. We present in this paper a new competitive genetic algorithm to solve this problem. This algorithm has been checked on a set of 153 benchmark instances with known optimal solution and it outperforms the results obtained with previous ATSP heuristic methods.

A way to optimally solve a time-dependent Vehicle Routing Problem with Time Windows

In this paper we deal with a generalization of the Vehicle Routing Problem with Time Windows that considers time-dependent travel times and costs. Through several steps we transform this extension into an Asymmetric Capacitated Vehicle Routing Problem, so it can be solved both optimally and heuristically with known codes.

The Rural Postman Problem on mixed graphs with turn penalties

In this paper we deal with a problem which generalizes the Rural Postman Problem defined on a mixed graph (MRPP). The generalization consists of associating a non-negative penalty to every turn as well as considering the existence of forbidden turns. This new problem fits real-world situations more closely than other simpler problems. A solution tour must traverse all the requiring service arcs and edges of the graph while not making forbidden turns. Its total cost will be the sum of the costs of the traversed arcs and edges together with the penalties associated with the turns done. The Mixed Rural Postman Problem with Turn Penalties (MRPPTP) consists of finding such a tour with a total minimum cost. We show that the new problem is NP-hard, even in some particular cases. In order to solve the MRPPTP, a polynomial transformation of the problem into the Asymmetric Traveling Salesman Problem (ATSP) can be done and then apply heuristics and exact methods for the ATSP. This transformation is summarized here and a specific heuristic algorithm, based on two recent heuristics for the MRPP, is also presented. Extensive computational experiments with more than 250 instances establish the effectiveness of our procedures.

An asymmetric TSP with time windows and with time-dependent travel times and costs: An exact solution through a graph transformation

In this paper we deal with an extended version of the Asymmetric Traveling Salesman Problem with Time Windows (ATSPTW) that considers time-dependent travel times and costs, for a more accurate approximation of some routing problems inside large cities, in which the time or cost of traversing certain streets (e.g. main avenues) depends on the moment of the day (for example rush-hours). Unlike other existing papers about time-dependent routing problems, we focus on an exact method for solving this new problem. For this end we first transform the problem into an Asymmetric Generalized TSP and then into a Graphical Asymmetric TSP. In this way, we can apply a known exact algorithm for the Mixed General Routing Problem, which seems to run well with our resulting instances. Computational results are presented on a set of 270 adapted instances from benchmark ATSPTW instances.

CtIP Silencing as a Novel Mechanism of Tamoxifen Resistance in Breast Cancer

Acquired resistance to the antiestrogen tamoxifen constitutes a major clinical challenge in breast cancer therapy. However, the mechanisms involved are still poorly understood. Using serial analysis of gene expression, we identified CtIP, a BRCA1- and CtBP-interacting protein, as one of the most significantly down-regulated transcripts in estrogen receptor α–positive (ER+) MCF-7 tamoxifen-resistant breast cancer cells. We further confirmed the association of CtIP down-regulation with tamoxifen resistance in an additional ER+ breast cancer line (T47D), strengthening the relevance of the phenomenon observed. In additional studies, we found CtIP protein expression in a majority of ER+ breast cancer cell lines that we tested, but no or very little CtIP expression in ER-negative lines. Furthermore, CtIP protein expression status correlates with clinical response to neoadjuvant endocrine therapy, and patients with progressive disease express significantly lower CtIP protein in their primary breast carcinomas than those who respond. Meta-analysis of seven publicly available gene expression microarray data sets showed that CtIP expression is significantly associated with ER, disease-free survival, and breast cancer metastasis status. Importantly, we found that silencing endogenous CtIP in tamoxifen-sensitive breast cancer cells confers tamoxifen resistance. On the other hand, reexpression of CtIP in tamoxifen-resistant breast cancer cells restores sensitivity to the inhibitory growth effects of tamoxifen. Together, our findings indicate that CtIP silencing might be a novel mechanism for the development of tamoxifen resistance in breast cancer, suggesting that CtIP is likely associated with ER function, and that CtIP gene and protein expression may be useful biomarkers for breast cancer prognosis and clinical management. (Mol Cancer Res 2007;5(12):1285–95)

A transformation for the mixed general routing problem with turn penalties

In this paper, we study a generalization of the Mixed General Routing Problem (MGRP) with turn penalties and forbidden turns. Thus, we present a unified model of this kind of extended versions for both node- and arc-routing problems with a single vehicle. We provide a polynomial transformation of this generalization into an asymmetric travelling salesman problem, which can be considered a particular case of the MGRP. We show computational results on the exact resolution on a set of 128 instances of the new problem using a recently developed code for the MGRP.

The mixed capacitated general routing problem with turn penalties

In this paper we deal with the mixed capacitated general routing problem with turn penalties. This problem generalizes many important arc and node routing problems, and it takes into account turn penalties and forbidden turns, which are crucial in many real-life applications, such as mail delivery, waste collection and street maintenance operations. Through a polynomial transformation of the considered problem into a Generalized Vehicle routing problem, we suggest a new approach for solving this new problem by transforming it into an Asymmetric Capacitated Vehicle routing problem. In this way, we can solve the new problem both optimally and heuristically using existing algorithms. A powerful memetic algorithm and a set of 336 new benchmark instances are also suggested. The experimental results show that the average deviation of the suggested solution method is less than 0.05% with respect to optimum.

Age-Structured Human Population Dynamics

ABSTRACT A von Foerster-McKendrick model to study age-structured human population dynamics is presented in this paper. Forecasts of population density (population per age unit) depending on ages are possible using this model. The model consists of a quasi-linear first order partial differential equation for the dynamics of population density per age-unit (except for the zero-age), a boundary condition for the births flow at zero-age, and an initial condition for the population density at the initial instant. A general solution independent of the particular human-system under study is obtained based on some hypotheses about the mathematical structure of its input variables. The model has been successfully applied to the case of the city of Valencia, Spain, for the time period 1991–2001.

The capacitated general windy routing problem with turn penalties

In this paper we present the capacitated general windy routing problem with turn penalties. This new problem subsumes many important and well-known arc and node routing problems, and it takes into account turn penalties and forbidden turns, which are crucial in many real-life applications, particularly in downtown areas and for large vehicles. We provide a way to solve this problem both optimally and heuristically by transforming it into a generalized vehicle routing problem.

A Stochastic Model for Population and Well-Being Dynamics

This article presents a stochastic dynamic model to study the demographic evolution per sexes and the corresponding well-being of a general human population. The main model variables are population per sexes and well-being. The considered well-being variable is the Gender-Related Development Index (GDI), a United Nations index. The models objectives are to improve future well-being and to reach a stable population in a country. The application case consists of adapting, validating, and using the model for Spain in the 2000–2006 period. Some instance strategies have been tested in different scenarios for the 2006–2015 period to meet these objectives by calculating the reliability of the results. The optimal strategy is “government invests more in education and maintains the present health investment tendency.”