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Search Results: 1 - 10 of 36241 matches for " Pascal Van Hentenryck "
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A Linear-Programming Approximation of AC Power Flows
Carleton Coffrin,Pascal Van Hentenryck
Mathematics , 2012,
Abstract: Linear active-power-only DC power flow approximations are pervasive in the planning and control of power systems. However, these approximations fail to capture reactive power and voltage magnitudes, both of which are necessary in many applications to ensure voltage stability and AC power flow feasibility. This paper proposes linear-programming models (the LPAC models) that incorporate reactive power and voltage magnitudes in a linear power flow approximation. The LPAC models are built on a convex approximation of the cosine terms in the AC equations, as well as Taylor approximations of the remaining nonlinear terms. Experimental comparisons with AC solutions on a variety of standard IEEE and MatPower benchmarks show that the LPAC models produce accurate values for active and reactive power, phase angles, and voltage magnitudes. The potential benefits of the LPAC models are illustrated on two "proof-of-concept" studies in power restoration and capacitor placement.
A constraint satisfaction approach to the robust spanning tree problem with interval data
Ionut Aron,Pascal Van Hentenryck
Computer Science , 2012,
Abstract: Robust optimization is one of the fundamental approaches to deal with uncertainty in combinatorial optimization. This paper considers the robust spanning tree problem with interval data, which arises in a variety of telecommunication applications. It proposes a constraint satisfaction approach using a combinatorial lower bound, a pruning component that removes infeasible and suboptimal edges, as well as a search strategy exploring the most uncertain edges first. The resulting algorithm is shown to produce very dramatic improvements over the mathematical programming approach of Yaman et al. and to enlarge considerably the class of problems amenable to effective solutions
Domain Views for Constraint Programming
Pascal Van Hentenryck,Laurent Michel
Computer Science , 2014,
Abstract: Views are a standard abstraction in constraint programming: They make it possible to implement a single version of each constraint, while avoiding to create new variables and constraints that would slow down propagation. Traditional constraint-programming systems provide the concept of {\em variable views} which implement a view of the type $y = f(x)$ by delegating all (domain and constraint) operations on variable $y$ to variable $x$. This paper proposes the alternative concept of {\em domain views} which only delegate domain operations. Domain views preserve the benefits of variable views but simplify the implementation of value-based propagation. Domain views also support non-injective views compositionally, expanding the scope of views significantly. Experimental results demonstrate the practical benefits of domain views.
A Microkernel Architecture for Constraint Programming
Laurent Michel,Pascal Van Hentenryck
Computer Science , 2014,
Abstract: This paper presents a microkernel architecture for constraint programming organized around a number of small number of core functionalities and minimal interfaces. The architecture contrasts with the monolithic nature of many implementations. Experimental results indicate that the software engineering benefits are not incompatible with runtime efficiency.
Sonet Network Design Problems
Marie Pelleau,Pascal Van Hentenryck,Charlotte Truchet
Electronic Proceedings in Theoretical Computer Science , 2009, DOI: 10.4204/eptcs.5.7
Abstract: This paper presents a new method and a constraint-based objective function to solve two problems related to the design of optical telecommunication networks, namely the Synchronous Optical Network Ring Assignment Problem (SRAP) and the Intra-ring Synchronous Optical Network Design Problem (IDP). These network topology problems can be represented as a graph partitioning with capacity constraints as shown in previous works. We present here a new objective function and a new local search algorithm to solve these problems. Experiments conducted in Comet allow us to compare our method to previous ones and show that we obtain better results.
Polynomial SDP Cuts for Optimal Power Flow
Hassan Hijazi,Carleton Coffrin,Pascal Van Hentenryck
Mathematics , 2015,
Abstract: The use of convex relaxations has lately gained considerable interest in Power Systems. These relaxations play a major role in providing global optimality guarantees for non-convex optimization problems. For the Optimal Power Flow (OPF) problem, the Semi-Definite Programming (SDP) relaxation is known to produce tight lower bounds. Unfortunately, SDP solvers still suffer from a lack of scalability. In this work, we introduce a new set of polynomial SDP-based constraints, strengthening weaker quadratic convex relaxations. The SDP cuts, expressed as polynomial constraints, can be handled by standard Nonlinear Programming solvers, enjoying better stability and computational efficiency. The new cut-generation procedure benefits from recent results on tree-decomposition methods, reducing the dimension of the underlying SDP matrices. As a side result, we present the first formulation of Kirchhoff's Voltage Law in the SDP space and reveal the existing link between these cycle constraints and the original SDP relaxation for three dimensional matrices. Numerical results on state-of-the- art benchmarks show a significant gain both in computational efficiency and optimality bound quality.
The Complexity of DC-Switching Problems
Karsten Lehmann,Alban Grastien,Pascal Van Hentenryck
Mathematics , 2014,
Abstract: This report provides a comprehensive complexity study of line switching in the Linear DC model for the feasibility problem and the optimization problems of maximizing the load that can be served (maximum switching flow, MSF) and minimizing generation cost (optimal transmission switching, OTS). Our results show that these problems are NP-complete and that there is no fully polynomial-time approximation scheme for planar networks with a maximum-node degree of 3. Additionally, we demonstrate that the problems are still NP-hard if we restrict the network structure to cacti with a maximum degree of 3. We also show that the optimization problems can not be approximated within any constant factor.
Strengthening the SDP Relaxation of AC Power Flows with Convex Envelopes, Bound Tightening, and Lifted Nonlinear Cuts
Carleton Coffrin,Hassan Hijazi,Pascal Van Hentenryck
Mathematics , 2015,
Abstract: This paper considers state-of-the-art convex relaxations for the AC power flow equations and introduces new valid cuts based on convex envelopes and lifted nonlinear constraints. These valid linear inequalities strengthen existing semidefinite and quadratic programming relaxations and dominate existing cuts proposed in the litterature. Together with model intersections and bound tightening, the new linear cuts close 8 of the remaining 13 open test cases in the NESTA archive for the AC Optimal Power Flow problem.
AC-Feasibility on Tree Networks is NP-Hard
Karsten Lehmann,Alban Grastien,Pascal Van Hentenryck
Mathematics , 2014,
Abstract: Recent years have witnessed significant interest in convex relaxations of the power flows, several papers showing that the second-order cone relaxation is tight for tree networks under various conditions on loads or voltages. This paper shows that AC-feasibility, i.e., to find whether some generator dispatch can satisfy a given demand, is NP-Hard for tree networks.
Simulation and Analysis of Container Freight Train Operations at Port Botany
Daniel Guimarans,Daniel Harabor,Pascal van Hentenryck
Computer Science , 2015,
Abstract: Over two million containers crossed the docks at Sydney's Port Botany in 2011/12; a figure that is forecast increase more than threefold by the end of the next decade. To cope with such large growth in volumes the NSW Government plans to double rail mode share at the port by the year 2020. Conventional wisdom from industry and the media says that existing infrastructure cannot handle such volumes. In this paper we use a combination of data analytics and simulation to examine operations at the port and evaluate the efficacy of current infrastructure to handle projected growth in volumes. Contrary to conventional wisdom we find that current rail resources appear distinctly under-utilised. Moreover: (i) the peak rail capacity of Port Botany is 1.78 million TEU per annum; over six times higher than 2011/12 rail volumes; (ii) there are no infrastructural impediments to the achievement of peak rail capacity; (iii) operational changes, not infrastructural investment, are the key to unlocking the potential of the port; (iv) Port Botany is well positioned to handle projected increases in container volumes over the next decade and beyond, including the 28% rail mode share target established by the New South Wales State Government.
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