Look-ahead Problem Research Articles

An online dynamic dual bin packing with lookahead approach for server-to-cell assignment in computer server industry

Efficient production scheduling in computer server industry remains a critical challenge. This challenge becomes particularly acute during the testing phase, where servers are assigned for testing in a modular environment consisting of test banks. Unique characteristics such as online arrival of servers known only over a short time window, skewed arrival pattern, power and cooling compatibility constraints, and dynamic assignment complicate decision making, a situation we observed at our industry partner’s site, which often leads to missing due dates and loss of customer trust. Motivated by this challenge, we introduce an Online Dynamic Dual Bin Packing with Lookahead problem and propose an integer linear programming model that maximizes the number of assigned servers. To efficiently solve this model, we decompose the problem into a set of subproblems for a given lookahead length. A ‘2-phase’ computational framework is proposed that seamlessly integrates mathematical programming with genetic algorithm. Based on realistic data available from a server manufacturer, our findings suggest that solutions are sensitive to (i) the length of the lookahead window, (ii) testing capacity and server arrival pattern, (iii) test processing time requirement, and (iv) physical allocation of servers.

The Representation of Gender and Inflectional Class in Italian: A Reply to Kučerová 2018

Kučerová (2018) puts forward a novel theory of the morphology and interpretation of nominal gender in Italian. Here, we take issue with this theory from both empirical and theoretical standpoints. We first show that several generalizations presented as empirical support for it are incorrect. We then point out three fundamental theoretical challenges. First, the proposed three-way classification of nouns does not represent the full range of facts, because it does not take into account plural morphology or the interdependencies of class and gender features. Second, the account of gender mismatch in terms of “semicon-servativity” fails to capture the Italian data, once the full paradigm is considered. Finally, the use of phase theory to model contextual valuation of gender faces an insurmountable lookahead problem.

Revisiting the Lookahead Effect in Mbe Reduplication

Due to its inherent nature of gradualness, Serial Template Satisfaction (STS, McCarthy et al. 2012) does not predict the existence of derivational lookahead, which is admitted by Base-Reduplicant (BR) Correspondence Theory (McCarthy & Prince 1995). In this regard, Wei & Walker (2020) show that STS cannot tackle the lookahead pattern in Mbe reduplication, where the amount of material copied is predetermined by a subsequent phonological change. This paper, however, offers an STS solution to resolve the derivational lookahead problem in Mbe.

A Lookahead Effect in Mbe Reduplication: Implications for Harmonic Serialism

Various phenomena involving the interaction of reduplication and phonology have been brought to bear on evaluating parallel versus serial theories of phonology. In Base-Reduplicant (BR) Correspondence Theory ( McCarthy and Prince 1995 ), implemented in the classic parallel version of Optimality Theory (P-OT; Prince and Smolensky 1993/2004 ), the mapping from the underlying representation to the surface output is direct, without intermediate stages. In P-OT, the candidate-generating function GEN can simultaneously introduce multiple changes to the input. In contrast, the theory of Serial Template Satisfaction (STS; McCarthy, Kimper, and Mullin (MKM) 2012 ) is an approach to reduplication couched within Harmonic Serialism ( McCarthy 2000 et seq .), a version of OT with serial evaluation that includes intermediate levels of structure. In Harmonic Serialism, GEN is restricted to making no more than one change at each derivational step, a property known as gradualness. An argument put forth in favor of STS is that it does not admit a number of reduplicative patterns that MKM claim are unattested, which are otherwise predicted by BR Correspondence Theory in P-OT ( MKM 2012:225 ). Among these are patterns formerly interpreted as overapplication, backcopying, and underapplication. While such patterns previously served as arguments for BR Correspondence Theory ( McCarthy and Prince 1995 , 1999 ), MKM reexamine those cases and conclude that they do not provide solid evidence against a serial approach. Among the remaining patterns, coda-skipping reduplication and derivational lookahead appear to offer the strongest arguments in favor of STS. These are the two patterns for which the parallel and serial versions of OT make quite distinct predictions. However, recent studies have called the status of arguments involving both patterns into question. Zukoff (2017) shows that STS does not actually exclude coda-skipping reduplication, because certain mechanics that STS employs to account for attested partial onset skipping would predict coda skipping. Adler and Zymet (2017) identify a reduplication pattern in Maragoli that poses a type of lookahead problem for STS: the ordering of reduplication and hiatus-driven glide formation depends on lookahead to the surface form of the reduplicant, which favors a simple onset. In light of the ongoing discussion on these issues, this squib focuses on another kind of lookahead effect in reduplication where the amount of material copied would depend on a subsequent phonological change in the setting of a serial evaluation. Due to the stepwise gradual change in Harmonic Serialism, STS predicts that lookahead effects are not possible, while the potential for multiple, simultaneous changes in P-OT predicts that they exist. In this squib, we argue that a reduplicative affixation in Mbe instantiates a lookahead effect—specifically, one that closely resembles a hypothetical pattern that MKM identify as a problem for STS, were it to be attested. Furthermore, the variation in reduplicant size is arguably a case of “simple-syllable reduplication,” a pattern claimed not to be predicted by STS. This reduplicative pattern in Mbe is straightforwardly accounted for in P-OT. However, in STS the pattern cannot be understood as a lookahead phenomenon, which gives rise to a treatment with unwanted stipulations and complications. We consider three alternatives in STS involving allomorphy or different templatic approaches, but find shortcomings in each.

Low-Dimensional Space- and Time-Coupled Power System Control Policies Driven by High-Dimensional Ensemble Weather Forecasts

Many predictive control problems can be solved at lower cost if the practitioner is able to make use of a high-dimensional forecast of exogenous uncertain quantities. For example, power system operators must accommodate significant short-term uncertainty in renewable energy infeeds. These are predicted using sophisticated numerical weather models, which produce an ensemble of scenarios for the evolution of atmospheric conditions. We describe a means of incorporating such forecasts into a multistage optimization framework able to make use of spatial and temporal correlation information. We derive an optimal procedure for reducing the size of the look-ahead problem by generating a low-dimensional representation of the uncertainty, while still retaining as much information as possible from the raw forecast data. We then demonstrate application of this technique to a model of the Great Britain grid in 2030, driven by the raw output of a real-world high-dimensional weather forecast from the U.K. Met Office. We also discuss applications of the approach beyond power systems.

PRO vs. Equi-DP

The purpose of this paper is to analyze how the established control sentences can be explained by Equi-DP analysis. For the Equi-DP analysis, three motivations are provided. Firstly, sentences are derived in a bottom-up fashion. Therefore, if we consider control sentences under minimalist syntax, a look-ahead problem arises since the pronominal PRO appears prior to its antecedent in the higher phrase. Secondly, unlike finite T, infinitival T has no tense feature, which means it cannot check any case. Finally, infinitval T doesn`t have EPP feature, so that a DP in the Spec-VP doesn`t move to Spec-TP. Under those assumptions, when a DP is merged in the embedded Spec-VP, this DP gets its thematic role by the embedded predicate. However, since infinitival T has neither tense nor EPP feature, the DP remains in the embedded Spec-VP but cannot check its case feature. Following Stroik`s Survive Principle, since the DP still needs its case feature checked, it survives in the numeration and ready for further syntactic operations. The same DP, so-called Equi-DP is remerged when the case-checking element appears in the derivation. When the derivation is complete and transfers to PF and LF interfaces, the DP gets its phonetic interpretation at its case-checking position and semantic interpretation at its thematic role checking position. Hence, under Equi-DP analysis, ad hoc explanation on control with PRO and null case is not required anymore.

Management of Kinetic and Electric Energy in Heavy Trucks

Trucks are responsible for the major part of inland freight and so, they are a backbone of the modern economy but they are also a large consumer of energy. In this context, a dominating vehicle is a truck with heavy load on a long trip. The aim with look-ahead control is to reduce the energy consumption of heavy vehicles by utilizing information about future conditions focusing on the road topography ahead of the vehicle. The possible gains with look-ahead control are evaluated by performing experiments with a truck on highway. A real-time control system based on receding horizon control (RHC) is set up where the optimization problem is solved repeatedly on-line for a certain horizon ahead of the vehicle. The experimental results show that significant reductions of the fuel consumption are achieved, and that the controller structure, where the algorithm calculates set points fed to lower level controllers, has satisfactory robustness to perform well on-board in a real environment. Moreover, the controller behavior has the preferred property of being intuitive, and the behavior is perceived as comfortable and natural by participating drivers and passengers. A well-behaved and efficient algorithm is developed, based on dynamic programing, for the mixed-integer nonlinear minimum-fuel problem. A modeling framework is formulated where special attention is given to properly include gear shifting with physical models. Fuel equivalents are used to reformulate the problem into a tractable form and to construct a residual cost enabling the use of a shorter horizon ahead of the vehicle. Analysis of errors due to discretization of the continuous dynamics and due to interpolation shows that an energy formulation is beneficial for reducing both error sources. The result is an algorithm giving accurate solutions with low computational effort for use in an on-board controller for a fuel-optimal velocity profile and gear selection. The prevailing approach for the look-ahead problem is RHC where main topics are the approximation of the residual cost and the choice of the horizon length. These two topics are given a thorough investigation independent of the method of solving the optimal control problem in each time step. The basis for the fuel equivalents and the residual cost is formed from physical intuition as well as mathematical interpretations in terms of the Lagrange multipliers used in optimization theory. Measures for suboptimality are introduced that enables choosing horizon length with the appropriate compromise between fuel consumption and trip time. Control of a hybrid electric powertrain is put in the framework together with control of velocity and gear. For an efficient solution of the minimum-fuel problem in this case, more fuel equivalence factors and an energy formulation are employed. An application is demonstrated in a design study where it is shown how the optimal trade-off between size and capacity of the electrical system depends on road characteristics, and also that a modestly sized electrical system achieves most of the gain. The contributions develop algorithms, create associated design tools, and carry out experiments. Altogether, a feasible framework is achieved that pave the way for on-board fuel-optimal look-ahead control.

On the Locality and Motivation of Move and Agree: An Even More Minimal Theory

The article proposes a new theory of successive-cyclic movement that reconciles the early and the current minimalist approaches to it. As in the early approach, there is no feature checking in intermediate positions of successive-cyclic movement. However, as in the current approach and unlike in early minimalism, successive-cyclic movement starts before the final target of movement enters the structure, and Form Chain is eliminated. The locality of Move and the locality of Agree are shown to be radically different, Agree being free from several mechanisms that constrain Move, namely, phases and the Activation Condition. However, there is no need to take phases to define locality domains of syntax or to posit the Activation Condition as an independent principle. They still hold empirically for Move as theorems. The Generalized EPP (the “I need a Spec” property of attracting heads) and the Inverse Case Filter are also dispensable. The traditional Case Filter, stated as a checking requirement, is the sole driving force of A-movement. More generally, Move is always driven by a formal inadequacy (an uninterpretable feature) of the moving element, while Agree is target driven. The system resolves a lookahead problem that arises under the EPP-driven movement approach, where the EPP diacritic indicating that X moves is placed on Y, not X, although X often needs to start moving before Y enters the structure.

A universal velocity profile generation approach for high-speed machining of small line segments with look-ahead

Usually a complex contour-machining program generated by CAD/CAM systems composes a lot of small line segments. The intelligence of look-ahead is key to meeting the demand of high speed and high accuracy in the machining of these line segments. By now most researchers just utilize the simplest trapezoidal velocity profiles to deal with the look-ahead problem. Also the number of look-ahead line segments in most commercially available CNC systems is fixed, which cannot make full use of CNC processors. Therefore, a universal velocity profiles generation approach and corresponding optimal look-ahead algorithm based on dynamic back tracking along a doubly linked list are proposed in this paper. Two novel strategies, one for reducing feed rates fluctuation and the other for reducing move errors that come from digital integration and accumulated computation, are also presented. By using the proposed look-ahead techniques, arbitrary velocity profiles having the desired acceleration and deceleration characteristics for the movement of a lot of small line segments can be generated efficiently. Thus, the machining productivity can be dramatically increased without sacrifice of accuracy. The results of simulations and experiments showed the proposed approach was feasible and effective.

Mealy machines are a better model of lexical analyzers

Lexical analyzers partition input characters into tokens. When ambiguities arise during lexical analysis, the longest-match rule is generally adopted to resolve the ambiguities. The longest-match rule causes the look-ahead problem in traditional lexical analyzers, which are based on Moore machines. In Moore machines, output tokens are associated with states of the automata. By contrast, because Mealy machines associate output tokens with state transitions, the look-ahead behaviors can be encoded in their state transition tables. Therefore, we believe that lexical analyzers should be based on Mealy machines, rather than Moore machines, in order to solve the look-ahead problem. We propose techniques to construct Mealy machines from regular expressions and to perform sequential and data-parallel lexical analysis with these Mealy machines.

On the look-ahead problem in lexical analysis

Modern programming languages use regular expressions to define valid tokens. Traditional lexical analyzers based on minimum deterministic finite automata for regular expressions cannot handle the l...

On the look-ahead problem in lexical analysis

Modern programming languages use regular expressions to define valid tokens. Traditional lexical analyzers based on minimum deterministic finite automata for regular expressions cannot handle the look-ahead problem. The scanner writer needs to explicitly identify the look-ahead states and code the buffering and re-scanning operations by hand. We identify the class of finite look-ahead finite automata, which is general enough to include all finite automata of practical lexical analyzers. Finite look-ahead finite automata are then transformed into suffix finite automata. A new lexical analyzer makes use of the suffix finite automata to identify tokens. The new lexical analyzer solves the look-ahead problem in a table-driven approach and it can detect lexical errors at an earlier time than traditional lexical analyzers. The extra cost of the new lexical analyzers is the larger state transition table and three additional 1-dimensional tables. Incremental lexical analysis is also discussed.

Efficient Computation of LALR(1) Look-Ahead Sets

Two relations that capture the essential structure of the problem of computing LALR(1) look-ahead sets are defined, and an efficient algorithm is presented to compute the sets in time linear in the size of the relations. In particular, for a PASCAL grammar, the algorithm performs fewer than 15 percent of the set unions performed by the popular compiler-compiler YACC. When a grammar is not LALR(1), the relations, represented explicitly, provide for printing useroriented error messages that specifically indicate how the look-ahead problem arose. In addition, certain loops in the digraphs induced by these relations indicate that the grammar is not LR(k) for any k. Finally, an oft-discovered and used but incorrect look-ahead set algorithm is similarly based on two other relations defined for the fwst time here. The formal presentation of this algorithm should help prevent its rediscovery.