Contractor Programming

WOSInternational audienceThis paper describes a solver programming method, called "contractor programming", that copes with two issues related to constraint processing over the reals. First, continuous constraints involve an inevitable step of solver design. Existing softwares provide an insufficient answer by restricting users to choose among a list of fixed strategies. Our first contribution is to give more freedom in solver design by introducing programming concepts where only configuration parameters were previously available. Programming consists in applying operators (intersection, composition, etc.) on algorithms called "contractors" that are somehow similar to propagators. Second, many problems with real variables cannot be cast as the search for vectors simultaneously satisfying the set of constraints, but a large variety of different outputs may be demanded from a set of constraints (e.g., a paving with boxes inside and outside of the solution set). These outputs can actually be viewed as the result of different "contractors" working concurrently on the same search space, with a bisection procedure intervening in case of deadlock. Such algorithms (which are not strictly speaking solvers) will be made easy to build thanks to a new branch & prune system, called "paver". Thus, this paper gives a way to deal harmoniously with a larger set of problems while giving a fine control on the solving mechanisms. The contractor formalism and the paver system are the two contributions. The approach is motivated and justified through different cases of study. An implementation of this framework named Quimper is also presented

Comprehensive Substance Abuse Prevention Program Evaluation: Annual Report 7/1/2016 – 6/30/2017,

The Iowa Consortium for Substance Abuse Research and Evaluation (Consortium) was awarded a contract with IDPH to evaluate the project and provide training and technical assistance to the providers on data collection and data entry. In addition, one contractor implemented prevention programming with early elementary students who are below the appropriate age for surveying; therefore, data for that contractor is not included in this report. Another contractor did not have access to schools for programming, so they do not have any surveys to include for this report. One contractor did not enter their post-tests by data cutoff thus their data are not included in this report

Global Optimization based on Contractor Programming

International audienceIn this paper, we will present a general pattern based on contractor programmingfor designing a global optimization solver. This approach allows to solve problems with awide variety of constraints. The complexity and the performance of the algorithm rely on theconstruction of contractors which characterize the feasible region

Bidding Strategy to Support Decision-Making Based on Comprehensive Information in Construction Projects

© 2016 Ru Liang et al. This paper develops a unified method to support contractor for bidding selection in construction projects. A cross-functional contractor with 28 candidate units distributed in the three departments (construction units, design units, and suppliers) is used as an example. This problem is first formulated as a 0-1 quadratic programming problem through optimizing individual performance and collaborative performance of the candidate units based on individual information and collaborative information. Then, a multiobjective evolutionary algorithm is designed to solve this problem and a bidding selection problem for a major bridge project is used to demonstrate our proposed method. The results show that the decision-maker (DM) obtains a better contractor if he pays more attention to collaborative performance

Client-contractor bargaining on net present value in project scheduling with limited resources

The client-contractor bargaining problem addressed here is in the context of a multi-mode resource constrained project scheduling problem with discounted cash flows, which is formulated as a progress payments model. In this model, the contractor receives payments from the client at predetermined regular time intervals. The last payment is paid at the first predetermined payment point right after project completion. The second payment model considered in this paper is the one with payments at activity completions. The project is represented on an Activity-on-Node (AON) project network. Activity durations are assumed to be deterministic. The project duration is bounded from above by a deadline imposed by the client, which constitutes a hard constraint. The bargaining objective is to maximize the bargaining objective function comprised of the objectives of both the client and the contractor. The bargaining objective function is expected to reflect the two-party nature of the problem environment and seeks a compromise between the client and the contractor. The bargaining power concept is introduced into the problem by the bargaining power weights used in the bargaining objective function. Simulated annealing algorithm and genetic algorithm approaches are proposed as solution procedures. The proposed solution methods are tested with respect to solution quality and solution times. Sensitivity analyses are conducted among different parameters used in the model, namely the profit margin, the discount rate, and the bargaining power weights

Client-contractor bargaining on net present value in project scheduling with limited resources

The client-contractor bargaining problem addressed here is in the context of a multi-mode resource constrained project scheduling problem with discounted cash flows, which is formulated as a progress payments model. In this model, the contractor receives payments from the client at predetermined regular time intervals. The last payment is paid at the first predetermined payment point right after project completion. The second payment model considered in this paper is the one with payments at activity completions. The project is represented on an Activity-on-Node (AON) project network. Activity durations are assumed to be deterministic. The project duration is bounded from above by a deadline imposed by the client, which constitutes a hard constraint. The bargaining objective is to maximize the bargaining objective function comprised of the objectives of both the client and the contractor. The bargaining objective function is expected to reflect the two-party nature of the problem environment and seeks a compromise between the client and the contractor. The bargaining power concept is introduced into the problem by the bargaining power weights used in the bargaining objective function. Simulated annealing algorithm and genetic algorithm approaches are proposed as solution procedures. The proposed solution methods are tested with respect to solution quality and solution times. Sensitivity analyses are conducted among different parameters used in the model, namely the profit margin, the discount rate, and the bargaining power weights

The Challenges and Obstacles of Post-Disaster Road Infrastructure Reconstruction in the Pre-Construction Phase

Purpose The reconstruction of road infrastructure in the post-disaster context require different approach when compared with road projects in the normal development context. Disaster recovery projects are seen as having their own unique identity, particularly due to stakeholder issues, resource challenges, capability issues, and even long-term reliability concerns. This paper invites a discussion regarding the challenges and obstacles identified in the reconstruction of road infrastructure in a post-disaster reconstruction setting, and focuses the discussion on the pre-construction phase. Design/ Methodology/ Approach The challenges and obstacles presented in this paper are based on the literature and the empirical evidence collected from the research in three case study districts in Aceh, Indonesia. Twenty-eight face-to-face semi-structured interviews were conducted with stakeholders of road infrastructure at the local, provincial and national level, and represented by respondents from the public works, planning agency, disaster management agency, consultant, contractors, and donor agencies. The findings were triangulated with the literature and consulted with five experts in the road infrastructure and disaster reconstruction area. Findings The identified challenges and obstacles are divided into three groups of discussion; planning and programming, road design, and procurement. Whilst some of these challenges are not unique to post-disaster context, the scale of the risks had been undermined. Originality/ value This paper identifies the challenges and obstacles of a road project in the post-disaster setting from the pre-construction perspective. Identification of these challenges and obstacles may help improve the implementation of post-disaster road infrastructure reconstruction projects in future recovery projects, particularly in the developing world

An application of the multi-depot heterogeneous fixed fleet open vehicle routing problem

This work describes an application of a multi-depot heterogeneous fixed fleet open vehicle routing problem. A contractor owns a fleet of vehicles with different capacities and running costs. The fleet is used to transport craftsmen from their homes to assigned project sites and back, with some of the craftsmen appointed as drivers while others are passengers. An optimisation model is described that enables the contractor to minimise the transportation costs, and a computational study shows that the model can be solved to optimality for realistically sized instances using a standard mixed-integer programming solver. A variant of the problem is also considered, where the assignment of craftsmen to projects is not fixed a priori. For this variant, several simple heuristic rules are investigated to generate project assignments, and computational results show that they are able to find improved assignments. Keywords: mixed integer programming, assignment, transportationsubmittedVersio

Vertical Merger Enforcement Actions: 1994–April 2020

We have revised our earlier listing of vertical merger enforcement actions by the Department of Justice and Federal Trade Commission since 1994. This revised listing includes 66 vertical matters beginning in 1994 through April 2020. It includes challenges and certain proposed transactions that were abandoned in the face of Agency concerns. This listing can be treated as an Appendix to Steven C. Salop and Daniel P. Culley, Revising the Vertical Merger Guidelines: Policy Issues and an Interim Guide for Practitioners, 4 JOURNAL OF ANTITRUST ENFORCEMENT 1 (2016)