Reasoning with imprecise trade-offs in decision making under certainty and uncertainty

In many real world situations, we make decisions in the presence of multiple, often conflicting and non-commensurate objectives. The process of optimizing systematically and simultaneously over a set of objective functions is known as multi-objective optimization. In multi-objective optimization, we have a (possibly exponentially large) set of decisions and each decision has a set of alternatives. Each alternative depends on the state of the world, and is evaluated with respect to a number of criteria. In this thesis, we consider the decision making problems in two scenarios. In the first scenario, the current state of the world, under which the decisions are to be made, is known in advance. In the second scenario, the current state of the world is unknown at the time of making decisions. For decision making under certainty, we consider the framework of multiobjective constraint optimization and focus on extending the algorithms to solve these models to the case where there are additional trade-offs. We focus especially on branch-and-bound algorithms that use a mini-buckets algorithm for generating the upper bound at each node of the search tree (in the context of maximizing values of objectives). Since the size of the guiding upper bound sets can become very large during the search, we introduce efficient methods for reducing these sets, yet still maintaining the upper bound property. We define a formalism for imprecise trade-offs, which allows the decision maker during the elicitation stage, to specify a preference for one multi-objective utility vector over another, and use such preferences to infer other preferences. The induced preference relation then is used to eliminate the dominated utility vectors during the computation. For testing the dominance between multi-objective utility vectors, we present three different approaches. The first is based on a linear programming approach, the second is by use of distance-based algorithm (which uses a measure of the distance between a point and a convex cone); the third approach makes use of a matrix multiplication, which results in much faster dominance checks with respect to the preference relation induced by the trade-offs. Furthermore, we show that our trade-offs approach, which is based on a preference inference technique, can also be given an alternative semantics based on the well known Multi-Attribute Utility Theory. Our comprehensive experimental results on common multi-objective constraint optimization benchmarks demonstrate that the proposed enhancements allow the algorithms to scale up to much larger problems than before. For decision making problems under uncertainty, we describe multi-objective influence diagrams, based on a set of p objectives, where utility values are vectors in Rp, and are typically only partially ordered. These can be solved by a variable elimination algorithm, leading to a set of maximal values of expected utility. If the Pareto ordering is used this set can often be prohibitively large. We consider approximate representations of the Pareto set based on ϵ-coverings, allowing much larger problems to be solved. In addition, we define a method for incorporating user trade-offs, which also greatly improves the efficiency

Selecting Strategies for Infinite-Horizon Dynamic LIMIDs

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Resistance and consciousness in Kenya and South Africa : A comparative study with particular reference to the novels of Ngugi wa Thiong'o and Alex La Guma.

This study undertakes an analysis of the models of response (resistance/(non-agency) to colonial, apartheid and post-colonial imposition which are posited in the novels of the Kenyan author Ngugi wa Thiong'o and the South African writer Alex La Guma. Such a focus involves related issues such as the relationship between the consciousness level of the subaltern and his/her capacity for resistance and how oppression affects self-construction and consciousness. Since the thesis deals with resistance and consciousness within the textual space of the novels, the central issue raised in the thesis is explored around questions of representations. In defining the nature of resistance literature, the introductory chapter characterises levels of resistance and distinguishes between "counter-hegemonic" and "combat" literature. Whereas "combat" literature tends to invert the colonial version of Manichean binarism and is placed squarely within the liberation struggle, "counter-hegemonic" fiction is defined as constituting the fragmented colonial subject and subverting the colonial representation of the subaltern without necessarily insisting on the implacable enmity of Manicheism and its location within the liberation struggle. Part 1 identifies Ngugi's A. Grain of Wheat and La Guma's A Walk in the Night and And A Threefold Cord as counter-hegemonic fiction. The texts may be viewed from two interconnected levels: the ambivalence and subversion of colonial discourse and the reconstruction of self in resistance to the colonial/apartheid/post-colonial domination. The texts fill the vacuum created by colonial discourse by defying the non-representation of the Other/the subaltern by writing about the world, culture and values absent in colonial representations, but the textual analyses reveal at the same time representations of the subaltern which resist essentialist representation of subaltern consciousness and reject an essentialist view of resistance as an obvious, non-contradictory act. In a brief chapter at the end of Part 1, the revised version of A Grain of Wheat is analysed, signalling Ngugi's transition from his counter-hegemonic to his combat phase. In Part 2 Ngugi's Devil on the Cross and Matigari and La Guma's In the Fog of the Seasons' End and Time of the Butcherbird are defined as "combat" fiction. In contrast to the novels discussed in Part 1, the texts under scrutiny in Part 2 expose essentialist assumptions about the colonial/apartheid/post-colonial situation. Ngugi and La Guma's literary projects focus on the urgency of the political situation in Kenya and South Africa, thereby underlining the ideological message in the texts and the importance of conscientising the subaltern. In the combat fiction of the two authors the emphasis is on a more direct, uncompromising and often one-dimensional reaction and struggle against the oppressor. While the thesis critiques certain aspects of this fairly fixed, one-dimensional representation of the African situation in these fictional texts, the thesis underlines the need for counter-narratives of freedom and liberation on the troubled African continent