Statistics and deterministic simulation models: Why not?

Statistical Methods;mathematische statistiek

Dynamic Lot Sizing and Scheduling in a Multi-Item Production System

In this research, algorithms are developed to address the problem of dynamic lot sizing and scheduling in a single level (or single operation) production system. This research deviates from previous research in this area in that it does not have the kind of assumptions regarding the real world production system that normally were made to reduce the complexity of the problem. Specifically, this research explicitly considers finite capacity, multiple items, known deterministic dynamic demand, sequence dependent setup times and setup costs, setup carryover and variable backlogging. The objective is to simultaneously determine the lot size and the sequence of production runs in each period to minimize the sum of setup, inventory, and backlogging costs. The research here is motivated by observations of a real world production system that has a highly automated operation with sequence dependent setup times. For problems of this kind, optimal solution algorithms do not yet exist and, therefore, heuristic solution algorithms are of interest. Two distinct approaches are proposed to address the problem. The first is a greedy approach that eliminates setups while potential savings are greater than the increase in inventory or backlogging costs incurred. The second approach solves the much easier single item problem optimally for each item and then adapts the solution to account for capacity constraints. An intelligent modification to the second approach is also tried where a overload penalty is used between successive runs of the single product optimization algorithms A common component of each approach is a dynamic programming algorithm implemented to determine the optimal sequence of production within each period and across the scheduling horizon. The addition of sequence dependent considerations introduces a traveling salesman type problem to the lot sizing and sequencing decisions. The algorithms have been tested over several combinations of demand and inventory related cost factors. Specifically the following factors at two levels each have been used: problem size, demand type, utilization, setup cost, backlogging cost, and backlogging limit. The test results indicate that, while the performance of the proposed algorithms appear to be affected by all the factors listed above, overall the regeneration algorithm with overload penalty outperforms all of the other algorithms at all factor level combinations. In summary, the contribution of this research has been the development of three new algorithms for dynamic lot sizing and scheduling of multiple items in a single level production system. Through extensive statistical analysis, it has been shown that these algorithms, in particular the regeneration algorithm with overload penalty , outperform the conventional scheduling techniques such as no lot sizing and economic manufacturing quantity

Structure out of sound

Thesis (Ph. D.)--Massachusetts Institute of Technology, Program in Media Arts & Sciences, 1993.Vita.Includes bibliographical references (p. 155-170).Michael Jerome Hawley.Ph.D

Essays on technical analysis in financial markets

Technical analysis is the study of price movements in traded markets so as to forecast future movements or identify trading opportunities. Following a review of the history and research of technical analysis, three empirical chapters evaluate a number of propositions popular among technical analysts. One approach used widely over the last century assumes that support and resistance levels can be predicted by projecting the ratios between the length and duration of successive trends, in particular using Fibonacci ratios like 1.618. This proposition is rejected for the Dow Jones Industrial Average by identifying turning points and testing for clustering by developing a block bootstrap procedure. A few significant ratios appear to support such anchoring by the market, but no more than would be expected by chance. The thesis then reports a survey based experiment that tests whether individuals themselves do have an in-built tendency to anchor forecasts of future trends on previous trends. The significance of the survey results are tested using a novel kernel density estimator based bootstrap methodology. Respondents' forecasts do bear some relationship to the size of the most recent trend by certain whole-number ratios by more often than would be expected by chance. The third experiment addresses the criticism that academic studies do not use a rich enough characterisation of technical analysis. 120 active market-timing strategies are tested using a regression based framework of equity fundamentals, macroeconomic fundamentals, behavioural variables and a diverse set of mainstream statistical indicators from technical analysis. Our recursive approach uses time-invariant rolling and expanding estimation windows as well as conditional windows based on the presence of structural breaks, identified using the conditional reverse ordered cusum method (ROC), of Pesaran and Timmermann (2002). Models that include both fundamental and technical indicators perform well, even allowing for realistic levels of transactions costs. And accounting for structural instability via the ROC method also improves performance

Extensions of simple eyeballing dynamic lot sizing heuristics

Computers and Operations Research256487-497CMOR

Novel Computing Paradigms using Oscillators

This dissertation is concerned with new ways of using oscillators to perform computational tasks. Specifically, it introduces methods for building finite state machines (for general-purpose Boolean computation) as well as Ising machines (for solving combinatorial optimization problems) using coupled oscillator networks.But firstly, why oscillators? Why use them for computation?An important reason is simply that oscillators are fascinating. Coupled oscillator systems often display intriguing synchronization phenomena where spontaneous patterns arise. From the synchronous flashing of fireflies to Huygens' clocks ticking in unison, from the molecular mechanism of circadian rhythms to the phase patterns in oscillatory neural circuits, the observation and study of synchronization in coupled oscillators has a long and rich history. Engineers across many disciplines have also taken inspiration from these phenomena, e.g., to design high-performance radio frequency communication circuits and optical lasers. To be able to contribute to the study of coupled oscillators and leverage them in novel paradigms of computing is without question an interesting andfulfilling quest in and of itself.Moreover, as Moore's Law nears its limits, new computing paradigms that are different from mere conventional complementary metal–oxide–semiconductor (CMOS) scaling have become an important area of exploration. One broad direction aims to improve CMOS performance using device technology such as fin field-effect transistors (FinFET) and gate-all-around (GAA) FETs. Other new computing schemes are based on non-CMOS material and device technology, e.g., graphene, carbon nanotubes, memristive devices, optical devices, etc.. Another growing trend in both academia and industry is to build digital application-specific integrated circuits (ASIC) suitable for speeding up certain computational tasks, often leveraging the parallel nature of unconventional non-von Neumann architectures. These schemes seek to circumvent the limitations posed at the device level through innovations at the system/architecture level.Our work on oscillator-based computation represents a direction that is different from the above and features several points of novelty and attractiveness. Firstly, it makes meaningful use of nonlinear dynamical phenomena to tackle well-defined computational tasks that span analog and digital domains. It also differs from conventional computational systems at the fundamental logic encoding level, using timing/phase of oscillation as opposed to voltage levels to represent logic values. These differences bring about several advantages. The change of logic encoding scheme has several device- and system-level benefits related to noise immunity and interference resistance. The use of nonlinear oscillator dynamics allows our systems to address problems difficult for conventional digital computation. Furthermore, our schemes are amenable to realizations using almost all types of oscillators, allowing a wide variety of devices from multiple physical domains to serve as the substrate for computing. This ability to leverage emerging multiphysics devices need not put off the realization of our ideas far into the future. Instead, implementations using well-established circuit technology are already both practical and attractive.This work also differs from all past work on oscillator-based computing, which mostly focuses on specialized image preprocessing tasks, such as edge detection, image segmentation and pattern recognition. Perhaps its most unique feature is that our systems use transitions between analog and digital modes of operation --- unlike other existing schemes that simply couple oscillators and let their phases settle to a continuum of values, we use a special type of injection locking to make each oscillator settle to one of the several well-defined multistable phase-locked states, which we use to encode logic values for computation. Our schemes of oscillator-based Boolean and Ising computation are built upon this digitization of phase; they expand the scope of oscillator-based computing significantly.Our ideas are built on years of past research in the modelling, simulation and analysis of oscillators. While there is a considerable amount of literature (arguably since Christiaan Huygens wrote about his observation of synchronized pendulum clocks in the 17th century) analyzing the synchronization phenomenon from different perspectives at different levels, we have been able to further develop the theory of injection locking, connecting the dots to find a path of analysis that starts from the low-level differential equations of individual oscillators and arrives at phase-based models and energy landscapes of coupled oscillator systems. This theoretical scaffolding is able not only to explain the operation of oscillator-based systems, but also to serve as the basis for simulation and design tools. Building on this, we explore the practical design of our proposed systems, demonstrate working prototypes, as well as develop the techniques, tools and methodologies essential for the process

Irrationality: What, Why and How

__Abstract__ This thesis has made a special effort to explore some relevant issues on (ir)rationality. Chapter 2 and Chapter 3 answer the question what is irrationality. Chapter 2 improves the methodology to measure irrationality by proposing a new incentive system on individual decision-making: the prior incentive system (Prince). Chapter 3 addresses the issue of irrationality in decisions under ambiguity. Chapter 4 answers the question of why we steer people away from irrationality. Chapter 4 discusses whether we should correct people's irrationality by imposing a better decision when freedom of choice cannot be realized. Chapter 4 concludes with recommending strong paternalism and provides a litmus test for people's views on paternalism. Chapter 5 answers the question how to make people less irrational. Chapter 5 studies the social influences on people's decision-making processes and offers possible approaches to nudge people away from irrationality

The dynamics of upward communication in organisations.

This study has researched the dynamics of upward communication within organisations through the rubric of ingratiation theory (Jones, 1964) and impression management (Goffman, 1955). Upward communication was explored via in-depth case studies, in a hundred and five semi-structured interviews across four organisations in Scotland. A qualitative, interpretive methodology was used. The interviews probed how upward communication was transmitted and investigated how ingratiation theory and impression management dynamics could impact on it by exploring the story telling (Gabriel, 200) and sense making approaches (Weick, 1995) employed by interviewees. The data was then tabulated on Excel sheets, using the Framework Analysis (Swallow et al., 2002), thus establishing an easily referenced, perfectly structured database. Finally, the data was sifted, perused, distilled and analysed interpretively. It was found that upward communication was shaped by processes such as downsizing, management and leadership styles, the power dynamics of the organisation, issues of publicness, and the perceived physical and psychological distance of the superior from the subordinate. Finally, the components of opinion conformity (a factor common to ingratiation theory and impression management), employee silence (Morrison and Milliken, 2000, Milliken, 2003), and cynicism (Fleming and Spicer, 2002; Naus, 2004, 2007) were identified as the most significant syndromes that impacted on the levels of upward communication within the four organisations. Hence, a Conformity/Silence/Cynicism model of upward communication (the CSC model) was devised as a means of illustrating the significance of the most important stimuli of upward communication that the study revealed. The issues raised in this study are fundamental to the theory and practice of management. Openness in the search for solutions to organisational problems is central to organisational learning. The creation of an organisational environment in which this is possible is therefore vital. This is the dominant context of this research