Multi-period pricing for perishable products : uncertainty and competition

Thesis (S.M.)--Massachusetts Institute of Technology, Computation for Design and Optimization Program, 2006.Includes bibliographical references (p. 107-109).The pricing problem in a multi-period setting is a challenging problem and has attracted much attention in recent years. In this thesis, we consider a monopoly and an oligopoly pricing problem. In the latter, several sellers simultaneously seek an optimal pricing policy for their products. The products are assumed to be differentiated and substitutable. Each seller has the option to set prices for her products at each time period, and her goal is to find a pricing policy that will yield the maximum overall profit. Each seller has a fixed initial inventory of each product to be allocated over the entire time horizon and does not have the option to produce additional inventory between periods. There are no holding costs or back-order costs. In addition, the products are perishable and have no salvage costs. This means that at the end of the entire time horizon, any remaining products will be worthless. The demand function each seller faces for each product is uncertain and is affected by both the prices at the current period and past pricing history for her and her competitors. In this thesis, we address both the uncertain and the competitive aspect of the problem. First, we study the uncertain aspect of the problem in a simplified setting, where there is only one seller and two periods in the model.(cont.) We use ideas of robust optimization, adjustable robust optimization, dynamic programming and stochastic optimization to find adaptable closed loop pricing policies. Theoretical and numerical results show how the budget of uncertainty, the presence of a reference price, delayed resource allocation, and feedback control affect the quality of the pricing policies. Second, we extend the model to a multi-period setting, where the computation becomes a major issue. We use a delayed constraint generation method to significantly increase the size of the problem that our models can handle. Finally, we consider the pricing problem in an oligopoly setting. We show the existence of solution for both the best response subproblem and the market equilibrium problem for all of the models we discuss in the thesis. We also consider an iterative learning algorithm and illustrate through simulations that an equilibrium pricing policy can be computed for all of our models.by Lei Zhang.S.M

Department of Electrical Engineering and Computer Science Records

The Electrical Engineering and Computer Science Department combines all aspects of electricity, electronics, hardware, and software into one multi-disciplinary unit, offering degree programs in Electrical Engineering and Computer Science with minors in Computer Science, Biomedical Engineering, and Software Engineering. This collection is composed of various materials pertaining to the Electrical Engineering and Computer Science Department. Included are brochures, programs, and newsletters

Digital assistance design for analog systems : digital baseband for outphasing power amplifiers

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (p. 145-150).Digital assistance is among many aspects that can be leveraged to help analog/mixed-signal designers keep up with the technology scaling. It usually takes the form of predistorter or compensator in an analog/mixed-signal system and helps compensate the nonidealities in the system. Digital assistance takes advantage of the process scaling with faster speed and a higher level of integration. When a digital system is co-optimized with system modeling techniques, digital assistance usually becomes a key enabling block for the high performance of the overall system. This thesis presents the design of digital assistances through the digital baseband design for outphasing power amplifiers. In the digital baseband design, this thesis conveys two major points: the importance of the use of the reduced-complexity system modeling techniques, and the communications between hardware design and system modeling. These points greatly help the success in the design of the energy-efficient baseband. The first part of the baseband design is to realize the nonlinear signal processing unit required by the modulation scheme. Conventional approaches of implementing this functionality do not scale well to meet the throughput, area and energy-efficiency targets. We propose a novel fixed-point piece-wise linear approximation technique for the nonlinear function computations involved in the signal processing unit. The new technique allows us to achieve an energy and area-efficient design with a throughput of 3.4Gsamples/s. Compared to the projected previous designs, our design shows 2x improvement in energy-efficiency and 25x in area-efficiency. The second part of the baseband design devotes to the nonlinear compensator design, aiming to improve the linearity performance of the outphasing power amplifier. We first explore the feasibility of a working compensator by use of an off-line iterative solving scheme. With the confirmation that a compensator does exist, we analyze the structure of the nonlinear baseband-equivalent PA system and create a dynamical real-time compensator model. The resulting compensator provides the overall PA system with around 10dB improvement in ACPR and up to 2.5% in EVM.by Yan Li.Ph.D

Feedback message passing for inference in Gaussian graphical models

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010.Includes bibliographical references (p. 89-92).For Gaussian graphical models with cycles, loopy belief propagation often performs reasonably well, but its convergence is not guaranteed and the computation of variances is generally incorrect. In this paper, we identify a set of special vertices called a feedback vertex set whose removal results in a cycle-free graph. We propose a feedback message passing algorithm in which non-feedback nodes send out one set of messages while the feedback nodes use a different message update scheme. Exact inference results can be obtained in O(k²n), where k is the number of feedback nodes and n is the total number of nodes. For graphs with large feedback vertex sets, we describe a tractable approximate feedback message passing algorithm. Experimental results show that this procedure converges more often, faster, and provides better results than loopy belief propagation.by Ying Liu.S.M

Better Type-Error Messages Through Lazy Typing

Producing precise and helpful error messages for type inference is still a challenge for implementations of functional languages. Current approaches often lack precision in terms of locating the origins of type errors. Moreover, suggestions for how to fix type errors that are offered by some tools are also often vague or incorrect. To address this problem we have developed a new approach to identifying type errors that is based on delaying typing decisions and systematically gathering context information to support the delayed decision making. Our technique, which we call lazy typing, is based on explicitly representing conflicting types and type errors in choice types that will be accumulated during the typing process. The structure of these types is then analyzed to produce error messages and, in many cases, also type-change suggestions. We will demonstrate that lazy typing is often more precise in locating type errors than existing tools and that it can also produce good type-change suggestions. We do not consider lazy typing as a replacement for other techniques, but rather as an addition that could help improve other approaches

A boundary element method with surface conductive absorbers for 3-D analysis of nanophotonics

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 127-132).Fast surface integral equation (SIE) solvers seem to be ideal approaches for simulating 3-D nanophotonic devices, as these devices generate fields both in an interior channel and in the infinite exterior domain. However, many devices of interest, such as optical couplers, have channels that cannot be terminated without generating reflections. Generating absorbers for these channels is a new problem for SIE methods, as the methods were initially developed for problems with finite surfaces. In this thesis, we show that the obvious approach for eliminating reflections, making the channel mildly conductive outside the domain of interest, is inaccurate. We propose a new method in which the absorber has gradually increasing surface conductivity; such an absorber can be easily incorporated in fast integral equation solvers. We present two types of PMCHW-based formulations to incorporate the surface conductivity into the SIE method. The accuracy of the two-type formulations are examined and discussed using an example of the scattering of a Mie sphere with surface conductivities. Moreover, we implement two different FFT-accelerated algorithms for the periodic non-absorbing region and the non-periodic absorbing region. In addition, we use perturbation theory and Poynting's theorem, respectively, to calculate the field decay rate due to the surface conductivity. We show a saturation phenomenon when the electrical surface conductivity is large. However, we show that the saturation is not a problem for the surface absorber since the absorber typically operates in a small surface conductivity regime. We demonstrate the effectiveness of the surface conductive absorber by truncating a rectangular waveguide channel. Numerical results show that this new method is orders of magnitude more effective than a volume absorber. We also show that the transition reflection decreases in a power law with increasing the absorber length. We further apply the surface conductive absorber to terminate a waveguide with period-a sinusoidally corrugated sidewalls. We show that a surface absorber that can perform well when the periodic waveguide system is excited with a large group-velocity mode may fail when excited with a smaller group-velocity mode, and give an asymptotic relation between the surface absorber length, transition reflections and group velocity. Numerical results are given to validate the asymptotic prediction.by Lei Zhang.Ph.D

Design and optimization of automotive power electronics utilizing FITMOS MOSFET technology

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 178-179).Power electronics are essential to many automotive applications, and their importance continues to grow as more vehicle functions incorporate electronic controls. MOSFETs are key elements in automotive power electronic circuits and MOSFET characteristics can strongly affect circuit size, cost and performance. Advances in MOSFET technology are thus of great importance to the advancement of automotive electronics. The new Floating Island and Thick Bottom Oxide Trench Gate MOSFET (FITMOS) developed at Toyota has tremendous potential for automobile applications due to its reduced on-resistance, improved temperature coefficient of resistance and reduced gate charge and input capacitance. In this research, we investigated the detailed characteristics of FITMOS devices, developed the SPICE model for simulation and explored their applications in the design of automotive power electronics. Specifically, we identified how to best utilize the FITMOS characteristics to benefit power circuit design and on quantifying the gains that can be achieved through their use. We also expose a previously unrecognized phenomenon in the FITMOS MOSFET. In particular, we show that the on-state resistance of the device depends on both frequency and on peak di/dt at a given frequency. This dynamic on resistance variation can have a significant application impact.by Wei Li.S.M

Mutant census : an empirical examination of the competent programmer hypothesis

Mutation analysis is often used to compare the effectiveness of different test suites or testing techniques. One of the main assumptions underlying this technique is the Competent Programmer Hypothesis, which proposes that programs are very close to a correct version, or that the difference between current and correct code for each fault is very small. Testers have generally assumed, on the basis of the Competent Programmer Hypothesis, that mutation analysis with single token changes produces mutations that are similar to real faults. While there exists some evidence that supports this assumption, these studies are based on analysis of a limited and potentially non-representative set of programs and are hence not conclusive. In this paper, we investigate the Competent Programmer Hypothesis by analyzing changes (and bug-fixes in particular) in a very large set of randomly selected projects using four different programming languages. Our analysis suggests that a typical fault involves about three to four tokens, and is seldom equivalent to any traditional mutation operator. We also find the most frequently occurring syntactical patterns, and identify the factors that affect the real bug-fix change distribution. Our analysis suggests that different languages have different distributions, which in turn suggests that operators optimal in one language may not be optimal for others. Moreover, our results suggest that mutation analysis stands in need of better empirical support of the connection between mutant detection and detection of actual program faults in a larger body of real programs.Keywords: testing tools, testing and debugging, empirical analysis, test frameworks, mutation operators, real fault