Rui Alves

Filtered and recovering beam search algorithms for the early/tardy scheduling problem with no idle time

In this paper, we present filtered and recovering beam search algorithms for the single machine earliness/tardiness scheduling problem with no idle time, and compare them with existing neighbourhood search and dispatch rule heuristics. Filtering procedures using both priority evaluation functions and problem-specific properties have been considered.The computational results show that the recovering beam search algorithms outperform their filtered counterparts, while the priority-based filtering procedure proves superior to the rules-based alternative. The best solutions are given by the neighbourhood search algorithm, but this procedure is computationally intensive and can only be applied to small or medium size instances. The recovering beam search heuristic provides results that are close in solution quality and is significantly faster, so it can be used to solve even large problems.

Improved heuristics for the early/tardy scheduling problem with no idle time

A dispatch rule and a greedy procedure are presented for the single machine earliness/tardiness scheduling problem with no idle time and compared with the best of the existing dispatch rules. Both dispatch rules use a lookahead parameter that had previously been set at a fixed value. We develop functions that map some instance statistics into appropriate values for that parameter. We also consider the use of dominance rules to improve the solutions obtained by the heuristics. The computational results show that the function-based versions of the heuristics outperform their fixed value counterparts and that the use of the dominance rules can indeed improve solution quality with little additional computational effort.

Beam search algorithms for the single machine total weighted tardiness scheduling problem with sequence-dependent setups

In this paper, we consider the single machine weighted tardiness scheduling problem with sequence-dependent setups. We present heuristic algorithms based on the beam search technique. These algorithms include classic beam search procedures, as well as the filtered and recovering variants. Previous beam search implementations use fixed beam and filter widths. We consider the usual fixed width algorithms, and develop new versions that use variable beam and filter widths. The computational results show that the beam search versions with a variable width are marginally superior to their fixed value counterparts, even when a lower average number of beam and filter nodes is used. The best results are given by the recovering beam search algorithms. For large problems, however, these procedures require excessive computation times. The priority beam search algorithms are much faster, and can therefore be used for the largest instances. Scope and purpose: We consider the single machine weighted tardiness scheduling problem with sequence-dependent setups. In the current competitive environment, it is important that companies meet the shipping dates, as failure to do so can result in a significant loss of goodwill. The weighted tardiness criterion is a standard way of measuring compliance with the due dates. Also, the importance of sequence-dependent setups in practical applications has been established in several studies. In this paper, we present several heuristics based on the beam search technique. In previous beam search implementations, fixed beam and filter widths have been used. We consider the usual fixed width algorithms, and also develop new versions with variable beam and filter widths. The computational tests show that the beam search versions with a variable width are marginally superior to their fixed value counterparts. The recovering beam search procedures are the heuristic of choice for small and medium size instances, but require excessive computation times for large problems. The priority beam search algorithm is the fastest of the beam search heuristics, and can be used for the largest instances.

An exact approach to early/tardy scheduling with release dates

In this paper, we consider the single machine earliness/tardiness scheduling problem with different release dates and no unforced idle time. The problem is decomposed into weighted earliness and weighted tardiness subproblems. Lower bounding procedures are proposed for each of these subproblems, and the lower bound for the original problem is the sum of the lower bounds for the two subproblems. The lower bounds and several versions of a branch-and-bound algorithm are then tested on a set of randomly generated problems, and instances with up to 30 jobs are solved to optimality. To the best of our knowledge, this is the first exact approach for the early/tardy scheduling problem with release dates and no unforced idle time.

Improved Lower Bounds for the Early/Tardy Scheduling Problem with No Idle Time

In this paper, we consider the single machine earliness/tardiness scheduling problem with no idle time. Two of the lower bounds previously developed for this problem are based on Lagrangean relaxation and the multiplier adjustment method, and require an initial sequence. We investigate the sensitivity of the lower bounds to the initial sequence, and experiment with different dispatch rules and some dominance conditions. The computational results show that it is possible to obtain improved lower bounds by using a better initial sequence. The lower bounds are also incorporated in a branch-and-bound algorithm, and the computational tests show that one of the new lower bounds has the best performance for larger instances.

Execution and pauses in writing narratives: Processing time, cognitive effort and typing skill

At the behavioural level, the activity of a writer can be described as periods of typing separated by pauses. Although some studies have been concerned with the functions of pauses, few have investigated motor execution periods. Precise estimates of the distribution of writing processes, and their cognitive demands, across periods of typing and pauses are lacking. Furthermore, it is uncertain how typing skill affects these aspects of writing. We addressed these issues, selecting writers of low and high typing skill who performed dictation and composition tasks. The occurrences of writing processes were assessed through directed verbalization, and their cognitive demands were measured through interference in reaction times (IRT). Before writing a narrative, 34 undergraduates learned to categorize examples of introspective thoughts as different types of activities related to writing (planning, translating, or revising). Then, while writing, they responded to random auditory probes, and reported their ongoing activity according to the learned categories. Convergent with previous findings, translating was most often reported, and revising and planning had fewer occurrences. Translating was mostly activated during motor execution, whereas revising and planning were mainly activated during pauses. However, none of the writing processes can be characterized as being typical of pauses, since translating was activated to a similar extent as the other two processes. Regarding cognitive demands, revising is likely to be the most demanding process in narrative writing. Typing skill had an impact on IRTs of motor execution. The demands of execution were greater in the low than in the high typing skill group, but these greater demands did not affect the strategy of writing processes activation. Nevertheless, low typing skill had a detrimental impact on text quality.

Cognitive processes in writing during pause and execution periods

The present study investigated how writing processes are activated during pause and execution periods. In two experiments, handwriting demands were manipulated by asking participants to compose with their familiar handwriting or with a high-demanding cursive uppercase calligraphy. Experiment 1 investigated narrative writing, a task with low planning demands. Experiment 2 addressed essay writing, a task with stronger planning demands. Occurrences of processes and their cognitive effort were analysed by asking participants to respond to random auditory probes and then to report their ongoing mental activity according to learned categories referring to the planning, translating, and revising writing processes. All together, the findings indicate that demands on planning did not affect how writing processes were activated during pauses and execution periods but automaticity of handwriting did. When handwriting was effortless, translating was mostly activated in parallel with motor execution, whereas revising and planning were mainly activated during pauses. However, none of the writing processes could be characterised as being typical of pauses, since translating was activated to a similar extent as the other two processes. By contrast, when handwriting was effortful, participants shifted to a more sequential functioning and activated translating mainly during pauses.

Beam search algorithms for the early/tardy scheduling problem with release dates

In this paper we consider the single machine earliness/tardiness scheduling problem with di?erent release dates and no unforced idle time. We present several heuristic algorithms based on the beam search technique. These algorithms include classical beam search procedures, with both priority and total cost evaluation functions, as well as the filtered and recovering variants. Both priority evaluation functions and problem-specific properties were considered for the filtering step used in the filtered and recovering beam search heuristics. Extensive preliminary tests were performed to determine appropriate values for the parameters used by each algorithm. The computational results show that the recovering beam search algorithms outperform their filtered counterparts in both solution quality and computational requirements, while the priority-based filtering procedure proves superior to the rules-based alternative. The beam search procedure with a total cost evaluation function provides very good results, but is computationally expensive and can therefore only be applied to small or medium size instances. The recovering algorithm is quite close in solution quality and is significantly faster, so it can be used to solve even large instances.

Heuristics for the single machine scheduling problem with quadratic earliness and tardiness penalties

In this paper, we consider the single machine scheduling problem with quadratic earliness and tardiness costs, and no machine idle time. We propose several dispatching heuristics, and analyse their performance on a wide range of instances. The heuristics include simple and widely used scheduling rules, as well as adaptations of those rules to a quadratic objective function. We also propose heuristic procedures that specifically address both the earliness and the tardiness penalties, as well as the quadratic cost function. Several improvement procedures were also analysed. These procedures are applied as an improvement step, once the heuristics have generated a schedule. The computational experiments show that the best results are provided by the heuristics that explicitly consider both early and tardy costs, and the quadratic objective function. Therefore, it is indeed important to specifically address the quadratic feature of the cost function, instead of simply using procedures originally developed for a linear objective function. The heuristics are quite fast, and are capable of quickly solving even very large instances. The use of an improvement step is recommended, since it usually improves the solution quality with little additional computational effort.

Influence of Typing Skill on Pause-Execution Cycles in Written Composition

It is well known that the cognitive cost of programming motor movements in writing can be considerably high if execution is not automatized. However, it is not clear how this cost might affect the on-line production of a written text, namely the distribution of pauses vs. execution periods. Narratives were collected using ScriptLog. Keystroke interval within a word was measured and used to distinguish between fast typists — for whom execution was presumably automatic, and slow typists — for whom execution required attention. The relative distribution of pauses vs. execution periods between two consecutive pauses was examined. Results showed that the time ratio between pauses and execution differs between groups. Relative to fast typists, slow typists make more pauses, and have shorter execution periods. These results are discussed in light of two phenomena: the trade-off between execution and formulation processes, and the adoption of serial vs. parallel ways of composing.