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Learning to branch with Tree-aware Branching Transformers

KNOWLEDGE-BASED SYSTEMS 2022年 252卷

作者： Lin, Jiacheng Zhu, Jialin Wang, Huangang Zhang, Tao Tsinghua Univ Dept Automat Beijing Peoples R China

Machine learning techniques have attracted increasing attention in learning Branch-and-Bound (B&B) variable selection policies, but most of the existing methods lack extensions to heterogeneous problems. Though parameterizing search trees has recently shown a promising alternative for het-erogeneous scenarios, it remains challenging to maintain good performance when generalizing to instances comparatively harder to solve than those seen during training. To fill this gap, we propose a tree-aware transformer-based branching framework for branching efficiently and effectively. Specifically, the transformer-based branching is conducted, in which the mutual connections between candidate variables can be evaluated by the self-attention mechanism. Then, we novelly encode the empirical data in the search tree, i.e., branching history, with a binary tree representation. In this way, we can fully utilize features exploited from the parameterized B&B search trees and stronger branching policies can be attained thereby. The proposed models are evaluated on multiple benchmark instances and achieve a significant boost on performance, in terms of smaller B&B search trees and lower primal-dual integrals and gaps for harder problems within a given time limit. Ablation studies further validate the effectiveness of our method. (c) 2022 Elsevier B.V. All rights reserved.

关键词： Branch and Bound Machine learning Branching strategies mixed integer linear programming

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Stochastic approach for economic viability of photovoltaic systems with battery storage for big electricity consumers in the regulated marketin Brazil

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ELECTRIC POWER SYSTEMS RESEARCH 2022年 205卷

作者： Lima, Delberis A. Feijao, Veronica Rodrigues Pontificia Univ Catolica Rio de Janeiro Rua Raul Pompeia 61-301 Rio De Janeiro Brazil

Today in Brazil, due to the government incentives, the Net-metering scheme can be seen as a Photovoltaic system that uses the power grid as a virtual battery. This analogy is possible due to the energy credits accumulated in the metering when the prosumer injects power to the network. When the government incentives run out, it can trigger an opportunity market to stimulate the consumers to have their own batteries. Associated with this, the Lithium-ion battery storage systems market has been promising due to a significant drop in battery prices in the last few *** work proposes a stochastic mixed integer linear programming (MILP) model to design a photovoltaic system integrated with battery energy storage, using generation and consumption scenarios under a Time-of-Use tariff model applied in Brazil. The decision variables are the number of panels, inverters, batteries, its daily operation and the power demand contracted. The objective function aims to minimize the annual cost of investment in photovoltaic system and battery as well as in electricity bill in the context of the Brazilian *** proposed model was adapted for a scheme with free export to the network and other with zero export in order to assess the importance of a storage system to keep the economic attraction of the photovoltaic system. Results indicated that the synergic effect of the photovoltaic system and battery, potentialize the arbitrage, which is related to the difference between peak and off-peak energy tariff, mainly with Zero Export scheme because the consumer is free to choose the capacity of the photovoltaic system, which is limited for Net-metering scheme.

关键词： Photovoltaic system Battery energy storage system Power demand contract Lithium -ion battery technology mixed integer linear programming Stochastic model Zero export system

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BESS Primary Frequency Control Strategies for the West Africa Power Pool

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ENERGIES 2022年第3期15卷

作者： Abayateye, Julius Corigliano, Silvia Merlo, Marco Zimmerle, Dan Colorado State Univ Energy Inst Dept Syst Engn Ft Collins CO 80523 USA Politecn Milan Dept Energy I-015146 Milan Italy

In recent years, power systems have been moving from conventional power plants toward the integration of renewable energy sources (RES). This trend is taking shape in many developing economies, including in the West Africa Power Pool (WAPP). The integration of RES, however, stresses grid security and stability due to the variability and intermittency of the underlying renewable sources. Battery Energy Storage Systems (BESS) have been identified as a possible solution to address the frequency control challenges in the WAPP Interconnected Transmission System (WAPPITS) in order to help to accommodate high levels of RES. This paper analyzes the application and effectiveness of BESS in providing primary frequency control reserves in the WAPPITS. The analyses are based on numerical simulations that were performed using an open-loop model based on historic frequency measurements from the WAPPITS. The simplified model provided a first-order analysis of the frequency control and state of charge (SOC) restoration logic for BESS installations. This study indicates that a droop-based control strategy that is able to react only to the symmetrical and fast frequency oscillations in the network could be appropriate for regulating BESS in the system. Moreover, it demonstrates that the deployment of BESS alone does not solve frequency control problems and a deep revision of the frequency control service is required, mainly involving traditional power plants.

关键词： Battery Energy Storage System (BESS) primary frequency control mixed integer linear programming renewable energy sources SOC restoration

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A Matheuristic based on Ant Colony System for the Combined Flexible Jobshop Scheduling and Vehicle Routing Problem *

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IFAC-PapersOnLine 2022年第10期55卷 1613-1618页

作者： William Torres-Tapia Jairo R. Montoya-Torres José Ruiz-Meza Sana Belmokhtar-Berraf Research Group on Logistics Systems Universidad de La Sabana km 7 autopista norte de Bogotá D.C. Chia Colombia COSYS-GRETTIA Université Gustave Eiffel ESIEE Paris 5 boulevard Descartes 77454 Champs-sur-Marne France

Nowadays, market behavior and globalization mean that end consumers are waiting very quickly for their orders to be delivered. This context forces companies to have high availability of finished products. For this reason, the industries that make up the supply chains are obliged to implement strategies to meet this customer need. One efficient practice is the integration of production and transportation activities. In the literature, few research works integrate the scheduling of production tasks with the vehicle routing. This paper aims at proposing a solution approach for the combined problem. The production system configuration is defined as a flexible jobshop, while the distribution problem is modeled as a vehicle routing problem. The proposed approach consists of two parts. First, production makespan is minimized through a hybrid algorithm based on ant colony system and local search. Then, the routing problem is solved optimally using mathematical programming in order to minimize the total travel time. Benchmark instances from the literature are adapted to deal with the combined problem. Experimental results show the efficiency and effectiveness of the proposed algorithm.

关键词： Flexible jobshop Vehicle Routing Problem Ant Colony Metaheuristic Local Search mixed integer linear programming

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Accelerating domain propagation: An efficient GPU-parallel algorithm over sparse matrices

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PARALLEL COMPUTING 2022年 109卷

作者： Sofranac, Boro Gleixner, Ambros Pokutta, Sebastian Berlin Insitute Technol Str 17 Juni 135 D-10623 Berlin Germany Zuse Inst Berlin Takustr 7 D-14195 Berlin Germany HTW Berlin Treskowallee 8 D-10318 Berlin Germany

center dot Currently, domain propagation in state-of-the-art MIP solvers is single thread only. center dot The paper presents a novel, efficient GPU algorithm to perform domain propagation. center dot Challenges are dynamic algorithmic behavior, dependency structures, sparsity patterns. center dot The algorithm is capable of running entirely on the GPU with no CPU involvement. center dot We achieve speed-ups of around 10x to 20x, up to 180x on favorably-large instances.

关键词： mixed integer linear programming MIP GPU Domain propagation Bound tightening Parallel algorithms

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Site-specific optimization of bus stop locations and designs over a corridor

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PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS 2022年 599卷

作者： Jin, Hui Liu, Yue Wu, Telan Zhang, Yanpei Soochow Univ Sch Rail Transportat 8 Jixue Rd Suzhou Jiangsu Peoples R China Univ Wisconsin Milwaukee Dept Civil & Environm Engn POB 784 Milwaukee WI 53201 USA

Bus stops, interfacing passenger demand with route design and traffic dynamics, play a critical role in improving bus operation efficiency. This study proposes a two-lane based link-node cell transmission model referring to bus stop length, for the optimization of bus stop locations and designs against car and bus demand as well as bus dwell time, along a corridor with sequent links of specific length, which are connected with signalized intersections and inserted with sparse or dense stops. Thus the effect on total travel time can be exploited of the complex relationship between traffic dynamics and continuous stops. The nonlinear modeling is then converted to mixed integer linear programming, which is solvable to optimality. Numerical analyses validate that the proposed stop configuration reduces total travel time under all cases, averaged to be 20.5% and 7.1% for the corridor with short and long links, respectively. The proposed scheme combines harbor-style and curb-side stops which may be far-side, mid-block, or near-side to coordinate bus and car flow, where MLC is reduced up to 32% on some links to alleviate capacity drop especially for the corridor with short links and dense stops, and DLC is increased up to 25% to enhance road utilization especially for the corridor with long links. This research provides insights on the designs and locations of bus stops along urban streets, to alleviate the conflicts between buses and cars for efficient and attractive bus service. (C) 2022 The Authors. Published by Elsevier B.V.

关键词： Bus stop mixed traffic flow Lane changing Two-lane cell transmission model mixed integer linear programming

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Coverage Path Planning Based on the Optimization Strategy of Multiple Solar Powered Unmanned Aerial Vehicles

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DRONES 2022年第8期6卷

作者： Le, Wenxin Xue, Zhentao Chen, Jian Zhang, Zichao China Agr Univ Coll Engn Beijing 100083 Peoples R China Jiangsu Univ Jiangsu Prov & Educ Minist Cosponsored Synergist Zhenjiang 212013 Jiangsu Peoples R China MNR Key Lab Spatial Temporal Big Data Anal & Applicat Shanghai 200063 Peoples R China Beihang Univ State Key Lab Virtual Real Technol & Syst Beijing 100191 Peoples R China

In some specific conditions, UAVs are required to obtain comprehensive information of an area or to operate in the area in an all-round way. In this case, the coverage path planning (CPP) is required. This paper proposes a solution to solve the problem of short endurance time in the coverage path planning (CPP) problem of multi-solar unmanned aerial vehicles (UAVs). Firstly, the energy flow efficiency based on the energy model is proposed to evaluate the energy utilization efficiency during the operation. Moreover, for the areas with and without obstacles, the coverage path optimization model is proposed based on the undirected graph search method. The constraint equation is defined to restrict the UAV from accessing the undirected graph according to certain rules. A mixed integer linear programming (MILP) model is proposed to determine the flight path of each UAV with the objective of minimizing operation time. Through the simulation experiment, compared with the Boustrophedon Cellular Decomposition method for coverage path planning, it is seen that the completion time is greatly improved. In addition, considering the impact of the attitude angle of the solar powered UAV when turning, the operation time and the total energy flow efficiency are defined as the optimization objective. The bi-objective model equation is established to solve the problem of the CPP. A large number of simulation experiments show that the optimization model in this paper selects different optimization objectives and applies to different shapes of areas to be covered, which has wide applicability and strong feasibility.

关键词： solar powered UAV energy flow efficiency coverage path planning mixed integer linear programming coverage path optimization model bi-objective optimization

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A methodology for the design and deployment of distributed cyber-physical systems for smart environments

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FUTURE GENERATION COMPUTER SYSTEMS-THE INTERNATIONAL JOURNAL OF ESCIENCE 2020年 109卷 420-430页

作者： Tanganelli, Giacomo Cassano, Luca Miele, Antonio Vallati, Carlo Univ Pisa Lungarno Pacinotti 43 I-56126 Pisa Italy Politecn Milan Pzza Leonardo Da Vinci 32 I-20133 Milan Italy

The pervasiveness and the growing processing capabilities of mobile and embedded computing systems are leading to a shift from the Internet of Things (IoT) paradigm to the Fog computing scenario where the environment is instrumented with high-performance computing in the proximity to cyber-physical systems. The design of such systems requires an accurate planning, on the one hand, to ensure that specific application requirements will be properly met at run-time, and, on the other hand, to minimize the system's monetary costs. In this paper we present a methodology for an automated design and deployment of distributed cyber-physical systems into smart environments. We propose an engine based on a mixed integer linear programming (MILP) formulation which takes in input a planimetry of the environment and a description of the applications and, based on a repository of available processing boards, identifies the cost-optimized instantiation of the processing architecture and the corresponding distribution of the application functionalities. By comparing our proposal with the existing methodologies that address similar problems we can highlight the following novelties: (i) we address a system architecture composed of heterogeneous devices, (ii) we adopt a realistic model of the environment, and (iii) we perform a joint co-exploration of architecture instantiation and applications mapping. An experimental evaluation, considering a smart office case study, demonstrates the potential of the proposed approach in minimizing the overall system monetary cost around 42% w.r.t. a baseline approach not exploiting planimetry information. Such results have been also confirmed by an extensive experimental campaign using synthetic problems, which also highlighted how the execution times of the optimization process are affordable for the design-time process. (C) 2020 Published by Elsevier B.V.

关键词： Distributed cyber-physical systems Smart environments mixed integer linear programming

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The selective traveling salesman problem with draft limits

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JOURNAL OF HEURISTICS 2020年第3期26卷 339-352页

作者： Gelareh, Shahin Gendron, Bernard Hanafi, Said Neamatian Monemi, Rahimeh Todosijevic, Raca Univ Artois IUT Bethune Dept Reseaux & Telecoms F-62000 Bethune France Univ Montreal Dept Informat & Rech Operat CP 6128Succursale Ctr Ville Montreal PQ H3C 3J7 Canada Univ Montreal CIRRELT CP 6128Succursale Ctr Ville Montreal PQ H3C 3J7 Canada Univ Polytech Hauts De France CNRS UMR 8201 LAMIH F-59313 Valenciennes 9 France Univ Southampton IT Innovat Ctr Southampton Hants England

This paper introduces the selective traveling salesman problem with draft limits, an extension of the traveling salesman problem with draft limits, wherein the goal is to design a maximum profit tour respecting draft limit constraints at the visited nodes. We propose a mixed integer linear programming (MILP) formulation for this problem. This MILP model is used to solve-to optimality-small size instances and to assess the quality of solutions obtained using a general variable neighborhood search heuristic that explores several neighborhood structures. Our extensive computational experiments confirm the efficiency of the method and the quality of the reported solutions.

关键词： Selective traveling salesman problem with draft limits Variable neighborhood search Location neighborhood structures Traveling salesman neighborhood structures mixed integer linear programming

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Multi-product continuous plant scheduling: combination of decomposition, genetic algorithm, and constructive heuristic

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INTERNATIONAL JOURNAL OF PRODUCTION RESEARCH 2020年第9期58卷 2677-2695页

作者： Borisovsky, Pavel Eremeev, Anton Kallrath, Josef Sobolev Inst Math Novosibirsk Russia BASF SE Ludwigshafen Germany

We propose a polylithic method for medium-term scheduling of a large-scale industrial plant operating in a continuous mode. The method combines a decomposition approach, a genetic algorithm (GA) and a constructive MILP-based heuristic. In the decomposition, decisions are made at two levels, using the rolling horizon approach. At the upper level, a reduced set of products and the time period is chosen to be considered in the lower level. At the lower level, a short-term scheduling MILP-model with event-based representation is used. A heuristic solution to the lower level problem is found using a constructive Moving Window heuristic guided by a genetic algorithm. The GA is applied for finding efficient utilisation of critical units in the lower level problem. For solving the one unit scheduling problem, a parallel dynamic programming algorithm is proposed. Implementation of the dynamic programming algorithm for a graphics processing unit (GPU) is incorporated in the GA for improving its performance. The experimental study of the proposed method on a real case of a large-scale plant shows a significant improvement of the solution quality and the solving time comparing to the pure decomposition algorithm proposed in the earlier study, and confirmed suitability of the proposed approach for the real-life production scheduling. In particular, the reduction of the number of changeovers and their duration in the obtained solution as well as the CPU time of solving the problem was about 60% using the new approach.

关键词： process planning mixed integer linear programming genetic algorithms dynamic programming greedy algorithms GPU polylithic approach

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