Robert N. Moll

A new extension of local search applied to the Dial-A-Ride Problem

Abstract In this paper we propose a cheap yet effective extension to the traditional local improvement algorithm. We present this extension in the context of the Dial-A-Ride Problem, a variant of the Traveling Salesman Problem. This extension, which we call sacrificing , yields significant improvements over its plain local improvement counterpart without adversely affecting the algorithms running time.

Programming Approach to Computability

1 Introduction.- 1.1 Partial Functions and Algorithms.- 1.2 An Invitation to Computability Theory.- 1.3 Diagonalization and the Halting Problem.- 2 The Syntax and Semantics of while-Programs.- 2.1 The Language of while-Programs.- 2.2 Macro Statements.- 2.3 The Computable Functions.- 3 Enumeration and Universality of the Computable Functions.- 3.1 The Effective Enumeration of while-Programs.- 3.2 Universal Functions and Interpreters.- 3.3 String-Processing Functions.- 3.4 Pairing Functions.- 4 Techniques of Elementary Computability Theory.- 4.1 Algorithmic Specifications.- 4.2 The s-m-n Theorem.- 4.3 Undecidable Problems.- 5 Program Methodology.- 5.1 An Invitation to Denotational Semantics.- 5.2 Recursive Programs 110 5.3* Proof Rules for Program Properties.- 6 The Recursion Theorem and Properties of Enumerations.- 6.1 The Recursion Theorem.- 6.2 Model-Independent Properties of Enumerations.- 7 Computable Properties of Sets (Part 1).- 7.1 Recursive and Recursively Enumerable Sets.- 7.2 Indexing the Recursively Enumerable Sets.- 7.3 Godels Incompleteness Theorem.- 8 Computable Properties of Sets (Part 2).- 8.1 Rices Theorem and Related Results.- 8.2 A Classification of Sets.- 9 Alternative Approaches to Computability.- 9.1 The Turing Characterization.- 9.2 The Kleene Characterization.- 9.3 Symbol-Manipulation Systems and Formal Languages.- References.- Notation Index.- Author Index.

Examples of hard tautologies in the propositional calculus

We present examples of hard tautologies in propositional calculus by encoding instances of the assertions made by Ramseys theorem. We provide evidence that these tautologies are indeed hard by 1. showing that there are no short proofs for these tautologies in certain restricted classes of proof systems; 2. relating a proof of these tautologies to the problem of determining the diagonal Ramsey numbers for graphs.

Program synthesis by analogy

By extending a given analogy, a known program which solves a given problem is converted to a program which solves a different but analogous problem. The domains of the two problems need not be the same but they must be related by an initial specified analogy. There are three features which distinguish the approach. First the analogy formation evolves gradually with the synthesis of the new program. Secondly the formation of the analogy is directed by the correctness proof of the known program. Finally the output of the synthesis process produces a correctness proof for the synthesized program.

An algorithm for the 2D guillotine cutting stock problem

Abstract The two-dimensional guillotine cutting stock problem seeks to apply a sequence of guillotine (edge to edge) cuts to extract a collection of smaller rectangles from a stock piece. In this paper an O(n3) approximation algorithm for the two-dimensional guillotine cutting stock problem is presented. The algorithm considers each rectangle, in turn, and attempts to locate a guillotine feasible position on the stock piece. The algorithm has the property that a position will be located for the n-th rectangle if and only if such a feasible placement exists. This paper establishes the efficiency and effectiveness of the new algorithm by presenting computational results.

New Results on the Analysis of Concurrent Systems with an Infinite Number of Processes

In this paper we extend some of the results presented by German and Sistla in [4]. Their framework for concurrent systems, at a certain level of abstraction, is suitable for modeling a number of resource-oriented problems in concurrency in which there is a unique control process (called the synchronizer) and an arbitrary number of identical user processes [13, 2]. Communication between processes is via synchronous actions in the style of Milner’s Calculus of Communicating Systems [12]. In the first part of the paper, we consider certain “specialized” execution semantics instead of the “general” execution semantics considered in [4]. These semantics are aimed at “restricting” communications between processes that would otherwise be possible. Without such restrictions, it is not possible to model problems in which there is a need to distinguish processes based on either the current states of the user processes, or their indices, etc. In contrast to the work done in [4], we show that the reachability problem for each of the specialized execution semantics we consider is undecidable. As a consequence, both deadlock detection and the Model Checking problem for the synchronizer when reasoning with logics such as Linear temporal logic LTL [4], Linear Temporal Logic without the nexttime operator LTL/X [8], and Restricted Temporal Logic RTL [14] are also undecidable.

Automated style feedback for advanced beginner Java programmers

We created an Eclipse plug-in called FrenchPress that offers students feedback on their Java programming style. It is designed not for novices but for students taking their second or third Java course. Advanced beginner students know enough to produce a program with the desired input/output behavior, but fail to understand it could still be poorly written. Large class sizes in introductory courses make it difficult for instructors to give their students individualized attention. FrenchPress automates a small subset of the feedback students might have received from educators. The system diagnoses issues characteristic of programmers who have not yet assimilated the object-oriented paradigm, such as misuse of the public modifier, fields that should have been local variables, and instance variables that should have been class constants. We conducted a classroom trial of the plug-in covering four assignments in data structures and algorithms. Among students whose code triggered one or more diagnostic rules, the percentage who modified their program in response to FrenchPress feedback varied from a high of 59% on the first project to a low of 23% on the second and fourth projects. On the user surveys following each assignment, 56-66% of respondents said they were satisfied with FrenchPress performance.

A specification-based approach to concurrency analysis

The behavior of a concurrent program often depends on the arbitrary interleaving of computations performed by asynchronous processes. The resulting non-determinism can lead to such phenomena as deadlock and starvation, making program development extremely difficult, and consequently making the development of tools for formal analysis highly desirable. A specification-based approach to concurrency analysis is a particularly promising way of addressing some of the difficulties inherent in concurrent program development. According to this approach, a programmer first writes a specification describing the interprocess communication behavior of a concurrent program. A set of formal analysis techniques are then applied in an effort to determine whether the specification can be fully satisfied. If the analysis is successful, target code is generated automatically that conforms to the specification. This approach has a variety of benefits. While such properties as safety and liveness are rather difficult to discern in actual code, they are actually easy to include as part of a specification. Moreover, state spaces induced by specifications tend to be smaller and more manageable than state spaces of actual code, and this leads to more effective analysis techniques. Finally, the generation of interprocess communication code from formal specifications is accomplished in a relatively straightforward manner.

Vector Sequence Analysis and Full Weak Safety for Concurrent Systems

In this paper we analyze a particular sequence of points in the poset of nonnegative lattice points in n-dimensions. For this sequence, in 2-dimensions, we obtain optimal upper bounds on the number of points to be selected in order to ensure desired chain lengths among selected points; for higher dimensions, the upper bounds obtained are not optimal [6]. We use these bounds to decide full weak safety for a simple resource-oriented model for concurrent systems ([5, 12]). In this model, processes execute a sequence of operations (a program) which are controlled by a finite state device called the synchronizer. Concurrency among processes is modeled as an interleaving of their operations. A concurrent system consisting of a synchronizer and infinitely many identical processes is full weak safe if and only if all valid interleavings (of any finite number of processes) are accepted by the synchronizer. To decide full weak safety, we use our chain length result to give an effective procedure to obtain a threshold τ, such that the model is full weak safe if and only if all interleavings of operations length τ or less are accepted by the synchronizer.

A Principled Approach to Solving Complex Discrete Optimization Problems

ABSTRACT In this work we report on a general and extensible framework, called OPL, for quickly constructing reasonable solutions to a broad class of complex discrete optimization problems. Our approach rests on the observation that many such problems can be represented by linking together variants of well-understood primitive optimization problems. We exploit this representation by building libraries of solution methods for the primitive problems. These library methods are then suitably composed to build solutions for the original problem. The vehicle routing problem and its generalizations, which involve not only routing but also delivery scheduling, crew scheduling, etc., is a significant and extensively investigated area of operations research. In this paper we report on OPL definitions and solutions for a wide variety of such problems.