A hybrid meta-heuristic optimization method is introduced to efficiently find the optimal shape of concrete gravity dams including dam-water-foundation rock interaction subjected to earthquake loading. The hybrid meta-heuristic optimization method is based on a hybrid of gravitational search algorithm (GSA) and particle swarm optimization (PSO), which is called GSA-PSO. The operation of GSA-PSO...

In general, a SAT Solver based on conflict-driven DPLL consists of variable selection, phase selection, Boolean Constraint Propagation, conflict analysis, clause learning and its database maintenance. Optimizing any part of these components can enhance the performance of a solver. This paper focuses on optimizing phase selection. Although the ACE (Approximation of the Combined lookahead Evaluat...

A phase transition refers to such a phenomenon of a system (or combinatorial problem) in which some global properties change rapidly and dramatically when a control parameter crosses a critical value. A simple example of phase transition is water changing phases from solid (ice) to liquid (water) to gas (steam) as the temperature increases. The backbone of a problem is the fraction of variables...

The Steiner tree problem is one of the classic and most fundamental NP-hard problems: given an arbitrary weighted graph, seek a minimum-cost tree spanning a given subset of the vertices (terminals). This article presents a two-phase heuristic in greedy strategy that achieves an approximation ratio of ≈ 1.430 for general graphs. Through combining the two-phase heuristic and the LP-based approxim...

We study the joint problem of scheduling passenger and freight trains for complex railway networks, where the objective is to minimize the tardiness of passenger trains at station stops and the delay of freight trains. We model the problem as a mixed integer program and propose a twostep decomposition heuristic to solve the problem. The heuristic first vertically decomposes the train schedules ...

This work describes a new best-first bidirectional heuristic search algorithm with two phases. The new algorithm is based on a critical review of the basic search reduction operations in previous algorithms like BS* or Switch-A*. The general guideline is to let search fronts meet as close to midground as possible. In a first phase, search is discontinued at nodes as soon as the opposite frontie...

This paper deals with the pickup and delivery traveling salesman problem. First we show how to adapt some classical traveling salesman heuristics to solve this problem, then we propose a new and e$cient composite heuristic. The proposed heuristic is composed of two phases: a solution construction phase including a local optimization component and a deletion and re-insertion improvement phase. T...