Squeaky Wheel Optimization

We describe a general approach to optimization which we term `Squeaky Wheel' Optimization (SWO). In SWO, a greedy algorithm is used to construct a solution which is then analyzed to find the trouble spots, i.e., those elements, that, if improved, are likely to improve the objective function score. The results of the analysis are used to generate new priorities that determine the order in which the greedy algorithm constructs the next solution. This Construct/Analyze/Prioritize cycle continues until some limit is reached, or an acceptable solution is found. SWO can be viewed as operating on two search spaces: solutions and prioritizations. Successive solutions are only indirectly related, via the re-prioritization that results from analyzing the prior solution. Similarly, successive prioritizations are generated by constructing and analyzing solutions. This `coupled search' has some interesting properties, which we discuss. We report encouraging experimental results on two domains, scheduling problems that arise in fiber-optic cable manufacturing, and graph coloring problems. The fact that these domains are very different supports our claim that SWO is a general technique for optimization

Flaw Selection Strategies for Partial-Order Planning

Several recent studies have compared the relative efficiency of alternative flaw selection strategies for partial-order causal link (POCL) planning. We review this literature, and present new experimental results that generalize the earlier work and explain some of the discrepancies in it. In particular, we describe the Least-Cost Flaw Repair (LCFR) strategy developed and analyzed by Joslin and Pollack (1994), and compare it with other strategies, including Gerevini and Schubert's (1996) ZLIFO strategy. LCFR and ZLIFO make very different, and apparently conflicting claims about the most effective way to reduce search-space size in POCL planning. We resolve this conflict, arguing that much of the benefit that Gerevini and Schubert ascribe to the LIFO component of their ZLIFO strategy is better attributed to other causes. We show that for many problems, a strategy that combines least-cost flaw selection with the delay of separable threats will be effective in reducing search-space size, and will do so without excessive computational overhead. Although such a strategy thus provides a good default, we also show that certain domain characteristics may reduce its effectiveness.Comment: See http://www.jair.org/ for an online appendix and other files accompanying this articl

Growth Characteristics Downstream of a Shallow Bump: Computation and Experiment

Measurements of the velocity field created by a shallow bump on a wall revealed that an energy peak in the spanwise spectrum associated with the driver decays and an initially small-amplitude secondary mode rapidly grows with distance downstream of the bump. Linear theories could not provide an explanation for this growing mode. The present Navier-Stokes simulation replicates and confirms the experimental results. Insight into the structure of the flow was obtained from a study of the results of the calculations and is presented

Bostonia. Volume 3

Founded in 1900, Bostonia magazine is Boston University's main alumni publication, which covers alumni and student life, as well as university activities, events, and programs

Defining a Task's Temporal Domain for Intelligent Calendar Applications

Abstract Intelligent calendar assistants have many years ago attracted research-ers from the areas of scheduling, machine learning and human computer interac-tion. However, all efforts have concentrated on automating the meeting schedul-ing process, leaving personal tasks to be decided manually by the user. Recently, an attempt to automate scheduling personal tasks within an electronic calendar application resulted in the deployment of a system called SELFPLANNER. The sys-tem allows the user to define tasks with duration, temporal domain and other attributes, and then automatically accommodates them within her schedule by employing constraint satisfaction algorithms. Both at the design phase and while using the system, it has been made clear that the main bottleneck in its use is the definition of a task’s temporal domain. To alleviate this problem, a new approach based on a combination of template application and manual editing has been de-signed. This paper presents the design choices underlying temporal domain defini-tion in SELFPLANNER and some computational problems that we had to deal with.

An Analysis of Conjunctive Goal Planning

This thesis develops a formal theory of planning, using a simple paradigm of planning that has been previously explored in work such as GPS, HACKER, STRIPS and NOAH. This thesis analyzes the goal interactions that occur when the goal is stated as a conjunction of subgoals. In this analysis we assume that the problem has a finite state space, and that operators are reversible. Graph theory can be used to characterize these subgoal interactions. The entire state space is treated as a graph, and each subgoal or conjunction of subgoals defines a subgraph. Each subgraph is composed of one or more connected components. Solving each subgoal by choosing a connected component that contains a final goal state is a necessary and sufficient condition for solving any planning problem. In the worst case, analyzing goal interactions is shown to be no more effective than enumerating the state space and searching. This complexity proves that no complete algorithm can solve all planning problems in linear time. The technique of goal ordering is analyzed, along with several extensions to that technique. While a generalization of goal ordering is possible, in the worst case generating the goal order requires as much computation as solving the problem by a brute-force search. A technique called capability analysis, derived from the connect component results, uses first-order logic to find the constraints that must apply as subgoals are achieved. A partial implementation uses counterfactual logic to identify the components of a world state that prevent the remaining subgoals from being achieved

Bostonia. Volume 4

Founded in 1900, Bostonia magazine is Boston University's main alumni publication, which covers alumni and student life, as well as university activities, events, and programs

Children\u27s Law Center Site Redevelopment

Soda City Engineering and Consulting was contracted by the USC School of Law to redevelop the Children’s Law Center site in Columbia, SC. Currently, the site does not comply with current standards and specifications. The objective of this project is to completely redevelop the site with a new annex building and ensuring everything is up to code, while still allowing the historic structure to maintain its use throughout construction