A particular problem concerning the efficient production of printed circuit boards in the electronics industry is addressed. It concerns the location of feeder bins which contain parts to be inserted in the boards. We...
详细信息
A particular problem concerning the efficient production of printed circuit boards in the electronics industry is addressed. It concerns the location of feeder bins which contain parts to be inserted in the boards. We address the question of identifying the optimal bin locations in order to determine the best insertion sequence of the parts. The location problem is formulated as a number of one-facility location models. The sequencing problem is formulated as a traveling salesman problem. Techniques are presented for these problems which accomodate a variety of distance norms and take into account the possibility of only certain feasible regions for the location of the bins.
We consider a time-varying network without parallel arcs and loops, where a flow must take a certain time to traverse an are. The transit time on an are and the capacity of an are are all time-varying parameters, whic...
详细信息
We consider a time-varying network without parallel arcs and loops, where a flow must take a certain time to traverse an are. The transit time on an are and the capacity of an are are all time-varying parameters, which depend on the departure time to traverse the are. To depart at the best time, a flow can wait at the beginning vertex of an are, which is however limited by a time-varying vertex capacity. All those parameters, namely, the transit time, the are capacity, and the vertex capacity, are discrete functions of time t. The problem is to find an optimal solution to send the maximum flow from the source vertex to the sink vertex, within a given time T. Moreover, we address the so-called universal maximum flow problem, which is to find a solution that remains optimal when the time limit T is truncated to any t less than or equal to T. We consider three variants of the problem, with waiting at a vertex being arbitrarily allowed, strictly prohibited, and bounded, respectively. Relevant algorithms are proposed, which can find optimal solutions in pseudopolynomial time. (C) 2001 Elsevier Science Ltd. All rights reserved.
Applications of dynamic programming (DP) to multicriteria sequential decision problems involving the optimization of a multicriteria preference function have been rare. This is due to the ease with which DP's mono...
详细信息
Applications of dynamic programming (DP) to multicriteria sequential decision problems involving the optimization of a multicriteria preference function have been rare. This is due to the ease with which DP's monotonicity assumption can be violated in such situations. Generalized DP avoids the potential pitfalls created by this absence of monotonicity, thereby guaranteeing optimality. The methodology is applied to a prototypical multicriteria DP problem, namely a multicriteria version of the shortest path problem. [ABSTRACT FROM AUTHOR]
Despite the efficiency shown by interior-point methods in large-scale linear programming, they usually perform poorly when applied to multicommodity ow problems. The new specialized interior-point algorithm presented ...
详细信息
Despite the efficiency shown by interior-point methods in large-scale linear programming, they usually perform poorly when applied to multicommodity ow problems. The new specialized interior-point algorithm presented here overcomes this drawback. This specialization uses both a preconditioned conjugate gradient solver and a sparse Cholesky factorization to solve a linear system of equations at each iteration of the algorithm. The ad hoc preconditioner developed by exploiting the structure of the problem is instrumental in ensuring the efficiency of the method. An implementation of the algorithm is compared to state-of-the-art packages for multicommodity flows. The computational experiments were carried out using an extensive set of test problems, with sizes of up to 700,000 variables and 150,000 constraints. The results show the effectiveness of the algorithm.
This work presents a new code for solving the multicommodity network flow problem with a linear or nonlinear objective function considering additional linear side constraints that link arcs of the same or different co...
详细信息
This work presents a new code for solving the multicommodity network flow problem with a linear or nonlinear objective function considering additional linear side constraints that link arcs of the same or different commodities. For the multicommodity network flow problem through primal partitioning the code implements a specialization of Murtagh and Saunders' strategy of dividing the set of variables into basic, nonbasic and superbasic. Several tests are reported, using random problems obtained from different network generators and real problems arising from the fields of long and short-term hydrothermal scheduling of electricity generation and traffic assignment, with sizes of up to 150 000 variables and 45 000 constraints. The performance of the code developed is compared to that of alternative methodologies for solving the same problems: a general purpose linear and nonlinear constrained optimization code, a specialised linear multicommodity network flow code and a primal-dual interior point coda.
Given n demand points on a plane, the problem we consider is to locate a given number, m, of facilities on the plane so that the maximum of the set of rectilinear distances of each demand point to its nearest facility...
详细信息
Given n demand points on a plane, the problem we consider is to locate a given number, m, of facilities on the plane so that the maximum of the set of rectilinear distances of each demand point to its nearest facility is minimized. This problem is known as the m-center problem on the plane. A related problem seeks to determine, for a given r, the minimum number of facilities and their locations so as to ensure that every point is within r units of rectilinear distance from its nearest facility. We formulate the latter problem as a problem of covering nodes by cliques of an intersection graph. Certain bounds are established on the size of the problem. An efficient algorithm is provided to generate this set-covering problem. Computational results with this approach are summarized. [ABSTRACT FROM AUTHOR]
In this paper we introduce a heuristic approach for the vehicle scheduling problem with sliding time windows. In the problem with time windows, we take advantage of the fact that the starting time of each task must fa...
详细信息
In this paper we introduce a heuristic approach for the vehicle scheduling problem with sliding time windows. In the problem with time windows, we take advantage of the fact that the starting time of each task must fall within a given time interval (i.e., a time window) rather than being fixed. Here, another level of flexibility is added by allowing the time windows of subsets of tasks to slide. The approach consists of identifying pairs of tasks offering good opportunity costs for reducing the overall cost, and finding ways of modifying the starting times to allow then to be linked. The technique is first developed for the problem with time windows and then extended to the case with sliding windows. Numerical results are reported to indicate the efficiency of the approach. [ABSTRACT FROM AUTHOR]
The paper deals with the fixed-time traffic control problem, which consists of finding a periodic schedule for the signals controlling the vehicular traffic in a system of intersections. A traffic model is used which ...
详细信息
The paper deals with the fixed-time traffic control problem, which consists of finding a periodic schedule for the signals controlling the vehicular traffic in a system of intersections. A traffic model is used which allows for constraints on green durations, conflicts and coordinations. The resulting mathematical model is formulated as ah extension of the feasible differential problem of network flow theory over a special graph associated with the intersection system. The fixed-time traffic control problem is proved to be NP-complete in general. A specialized algorithm is proposed for its solution; moreover, an alternative solution method based on mixed-integer linear programming is given. Finally, a real example is modelled and solved. [ABSTRACT FROM AUTHOR]
In the last decade, many calculi for modelling distributed mobile code have been proposed. To assess their merits and encourage use, implementations of the calculi have often been proposed. These implementations usual...
详细信息
In the last decade, many calculi for modelling distributed mobile code have been proposed. To assess their merits and encourage use, implementations of the calculi have often been proposed. These implementations usually consist of a limited part dealing with mechanisms that are specific of the proposed calculus and of a significantly larger part handling recurrent mechanisms that are common to many calculi. Nevertheless, also the "classic" parts are often re-implemented from scratch. In this paper we show how to implement a well established representative of the family of mobile calculi, the distributed pi-calculus, by using a Java middleware (called IMC - Implementing Mobile Calculi) where recurrent mechanisms of distributed and mobile systems are already implemented. By means of the case study, we illustrate a methodology to accelerate the development of prototype implementations while concentrating only on the features that are specific of the calculus under consideration and relying on the common framework for all the recurrent mechanisms like network connections, code mobility, name handling, etc.
In this paper we are concerned with a special class of bicriterion path problems. For the considered class of bicriterion problems at least one of the objectives is type MAXMIN. For the other one, besides an objective...
详细信息
In this paper we are concerned with a special class of bicriterion path problems. For the considered class of bicriterion problems at least one of the objectives is type MAXMIN. For the other one, besides an objective type MAXMIN also a MINSUM and a MINRATIO type objective are considered. Two algorithms are presented for the considered class of bicriterion path problems. The first one only determines the minimal complete set of nondominated paths and the second one determines the entire set of non-dominated paths. Both algorithms can be used for any type of bicriterion path problems, since one of the objectives is type MAXMIN and an algorithm exists to determine the best path for the other objective. Computational statistics for the three types of considered bicriterion path problems are also presented. [ABSTRACT FROM AUTHOR]
暂无评论