Pseudonormality and a language multiplier theory for constrained optimization

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2003.Includes bibliographical references (leaves 211-213).Lagrange multipliers are central to analytical and computational studies in linear and non-linear optimization and have applications in a wide variety of fields, including communication, networking, economics, and manufacturing. In the past, the main research in Lagrange multiplier theory has focused on developing general and easily verifiable conditions on the constraint set, called constraint qualifications, that guarantee the existence of Lagrange multipliers for the optimization problem of interest. In this thesis, we present a new development of Lagrange multiplier theory that significantly differs from the classical treatments. Our objective is to generalize, unify, and streamline the theory of constraint qualifications. As a starting point, we derive an enahanced set of necessary optimality conditions of the Fritz John-type, which are stronger than the classical Karush-Kuhn-Tucker conditions. They are also more general in that they apply even when there is a possibly nonconvex abstract set constraint, in addition to smooth equality and inequality constraints. These optimality conditions motivate the introduction of a new condition, called pseudonormality, which emerges as central within the taxonomy of significant characteristics of a constraint set. In particular, pseudonormality unifies and extends the major constraint qualifications. In addition, pseudonormality provides the connecting link between constraint qualifications and exact penalty functions. Our analysis also yields identification of different types of Lagrange multipliers. Under some convexity assumptions, we show that there exists a special Lagrange multiplier vector, called informative, which carries significant sensitivity information regarding the constraints that directly affect the optimal cost change.(cont.) In the second part of the thesis, we extend the theory to nonsmooth problems under convexity assumptions. We introduce another notion of multiplier, called geometric, that is not tied to a specific optimal solution and does not require differentiability of the cost and constraint functions. Using a line of development based on convex analysis, we develop Fritz John-type optimality conditions for problems that do not necessarily have optimal solutions. Through an extended notion of constraint pseudonormality, this development provides an alternative pathway to strong duality results of convex programming. We also introduce special geometric multipliers that carry sensitivity information and show their existence under very general conditions.by Asuman E. Ozdaglar.Ph.D

Diffusion of innovations in social networks

While social networks do affect diffusion of innovations, the exact nature of these effects are far from clear, and, in many cases, there exist conflicting hypotheses among researchers. In this paper, we focus on the linear threshold model where each individual requires exposure to (potentially) multiple sources of adoption in her neighborhood before adopting the innovation herself. In contrast with the conclusions in the literature, our bounds suggest that innovations might spread further across networks with a smaller degree of clustering. We provide both analytical evidence and simulations for our claims. Finally, we propose an extension for the linear threshold model to better capture the notion of path dependence, i.e., a few minor shocks along the way could alter the course of diffusion significantly.Charles Stark Draper Laboratory. Independent Research and Development. University Research & DevelopmentNational Science Foundation (U.S.). (Grant number SES-0729361)United States. Air Force Office of Scientific Research (Grant number FA9550-09-1-0420)United States. Air Force Office of Scientific Research. (Grant number W911NF-09-1-0556

Experimentation, patents, and innovation

October 8, 200

Value of Information in Bayesian Routing Games

We study a routing game in an environment with multiple heterogeneous information systems and an uncertain state that affects edge costs of a congested network. Each information system sends a noisy signal about the state to its subscribed traveler population. Travelers make route choices based on their private beliefs about the state and other populations' signals. The question then arises, "How does the presence of asymmetric and incomplete information affect the travelers' equilibrium route choices and costs?'' We develop a systematic approach to characterize the equilibrium structure, and determine the effect of population sizes on the relative value of information (i.e. difference in expected traveler costs) between any two populations. This effect can be evaluated using a population-specific size threshold. One population enjoys a strictly positive value of information in comparison to the other if and only if its size is below the corresponding threshold. We also consider the situation when travelers may choose an information system based on its value, and characterize the set of equilibrium adoption rates delineating the sizes of subscribed traveler populations. The resulting routing strategies are such that all travelers face an identical expected cost and no traveler has the incentive to change her subscription

Asynchronous CSMA Policies in Multihop Wireless Networks With Primary Interference Constraints

We analyze asynchronous carrier sense multiple access (CSMA) policies for scheduling packet transmissions in multihop wireless networks subject to collisions under primary interference constraints. While the (asymptotic) achievable rate region of CSMA policies for single-hop networks has been well-known, their analysis for general multihop networks has been an open problem due to the complexity of complex interactions among coupled interference constraints. Our work resolves this problem for networks with primary interference constraints by introducing a novel fixed-point formulation that approximates the link service rates of CSMA policies. This formulation allows us to derive an explicit characterization of the achievable rate region of CSMA policies for a limiting regime of large networks with a small sensing period. Our analysis also reveals the rate at which CSMA achievable rate region approaches the asymptotic capacity region of such networks. Moreover, our approach enables the computation of approximate CSMA link transmission attempt probabilities to support any given arrival vector within the achievable rate region. As part of our analysis, we show that both of these approximations become (asymptotically) accurate for large networks with a small sensing period. Our numerical case studies further suggest that these approximations are accurate even for moderately sized networks.United States. Defense Threat Reduction Agency (Grant number HDTRA 1-08-1-0016)National Science Foundation (U.S.). (CAREER-CNS-0953515)National Science Foundation (U.S.). (CCF-0916664