On reducing the complexity of matrix clocks

Matrix clocks are a generalization of the notion of vector clocks that allows the local representation of causal precedence to reach into an asynchronous distributed computation's past with depth $x$, where $x\ge 1$ is an integer. Maintaining matrix clocks correctly in a system of $n$ nodes requires that everymessage be accompanied by $O(n^x)$ numbers, which reflects an exponential dependency of the complexity of matrix clocks upon the desired depth $x$. We introduce a novel type of matrix clock, one that requires only $nx$ numbers to be attached to each message while maintaining what for many applications may be the most significant portion of the information that the original matrix clock carries. In order to illustrate the new clock's applicability, we demonstrate its use in the monitoring of certain resource-sharing computations

Coordination of Multirobot Systems Under Temporal Constraints

Multirobot systems have great potential to change our lives by increasing efficiency or decreasing costs in many applications, ranging from warehouse logistics to construction. They can also replace humans in dangerous scenarios, for example in a nuclear disaster cleanup mission. However, teleoperating robots in these scenarios would severely limit their capabilities due to communication and reaction delays. Furthermore, ensuring that the overall behavior of the system is safe and correct for a large number of robots is challenging without a principled solution approach. Ideally, multirobot systems should be able to plan and execute autonomously. Moreover, these systems should be robust to certain external factors, such as failing robots and synchronization errors and be able to scale to large numbers, as the effectiveness of particular tasks might depend directly on these criteria. This thesis introduces methods to achieve safe and correct autonomous behavior for multirobot systems. Firstly, we introduce a novel logic family, called counting logics, to describe the high-level behavior of multirobot systems. Counting logics capture constraints that arise naturally in many applications where the identity of the robot is not important for the task to be completed. We further introduce a notion of robust satisfaction to analyze the effects of synchronization errors on the overall behavior and provide complexity analysis for a fragment of this logic. Secondly, we propose an optimization-based algorithm to generate a collection of robot paths to satisfy the specifications given in counting logics. We assume that the robots are perfectly synchronized and use a mixed-integer linear programming formulation to take advantage of the recent advances in this field. We show that this approach is complete under the perfect synchronization assumption. Furthermore, we propose alternative encodings that render more efficient solutions under certain conditions. We also provide numerical results that showcase the scalability of our approach, showing that it scales to hundreds of robots. Thirdly, we relax the perfect synchronization assumption and show how to generate paths that are robust to bounded synchronization errors, without requiring run-time communication. However, the complexity of such an approach is shown to depend on the error bound, which might be limiting. To overcome this issue, we propose a hierarchical method whose complexity does not depend on this bound. We show that, under mild conditions, solutions generated by the hierarchical method can be executed safely, even if such a bound is not known. Finally, we propose a distributed algorithm to execute multirobot paths while avoiding collisions and deadlocks that might occur due to synchronization errors. We recast this problem as a conflict resolution problem and characterize conditions under which existing solutions to the well-known drinking philosophers problem can be used to design control policies that prevents collisions and deadlocks. We further provide improvements to this naive approach to increase the amount of concurrency in the system. We demonstrate the effectiveness of our approach by comparing it to the naive approach and to the state-of-the-art.PHDElectrical Engineering: SystemsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/162921/1/ysahin_1.pd

The combinatorics of resource sharing

We discuss general models of resource-sharing computations, with emphasis on the combinatorial structures and concepts that underlie the various deadlock models that have been proposed, the design of algorithms and deadlock-handling policies, and concurrency issues. These structures are mostly graph-theoretic in nature, or partially ordered sets for the establishment of priorities among processes and acquisition orders on resources. We also discuss graph-coloring concepts as they relate to resource sharing.Comment: R. Correa et alii (eds.), Models for Parallel and Distributed Computation, pp. 27-52. Kluwer Academic Publishers, Dordrecht, The Netherlands, 200

Working in Development Ethics - a tribute to Denis Goulet

ABSTRACT Denis Goulet (1931-2006) was probably the main founder of work on ‘development ethics’ as a self-conscious field that treats the ethical and value questions posed by development theory, planning and practice. This overview of a selection of papers presented at a conference of the International Development Ethics Association (Uganda, 2006) surveys Goulet’s work and compares it with issues and approaches in the selected papers. Ideas raised by Goulet provide a framework for discussing the set of papers, which especially consider corruption, professional ethics and the rights to water and essential drugs. The papers in turn provide a basis for comparing Goulet’s ideas with actual directions of work on development ethics. Rather than as a separate sub-discipline, development ethics takes shape as an interdisciplinary meeting place, aided though by the profile and intellectual space that Goulet strikingly strove to build for it

Introduction: Working in Development Ethics – a tribute to Denis Goulet

Denis Goulet (1931-2006) was probably the main founder of work on ‘development ethics’ as a self-conscious field that treats the ethical and value questions posed by development theory, planning and practice. This overview of a selection of papers presented at a conference of the International Development Ethics Association (Uganda, 2006) surveys Goulet’s work and compares it with issues and approaches in the selected papers. Ideas raised by Goulet provide a framework for discussing the set of papers, which especially consider corruption, professional ethics and the rights to water and essential drugs. The papers in turn provide a basis for comparing Goulet’s ideas with actual directions of work on development ethics. Rather than as a separate sub-discipline, development ethics takes shape as an interdisciplinary meeting place, aided though by the profile and intellectual space that Goulet strikingly strove to build for it

Where do preferences come from?

Rational choice theory analyzes how an agent can rationally act, given his or her preferences, but says little about where those preferences come from. Preferences are usually assumed to be fixed and exogenously given. Building on related work on reasons and rational choice (Dietrich and List, Nous, forthcoming), we describe a framework for conceptualizing preference formation and preference change. In our model, an agent’s preferences are based on certain ‘motivationally salient’ properties of the alternatives over which the preferences are held. Preferences may change as new properties of the alternatives become salient or previously salient properties cease to be salient. Our approach captures endogenous preferences in various contexts and helps to illuminate the distinction between formal and substantive concepts of rationality, as well as the role of perception in rational choice

Where do preferences come from?

Rational choice theory analyzes how an agent can rationally act, given his or her preferences, but says little about where those preferences come from. Instead, pref- erences are usually assumed to be �xed and exogenously given. Building on related work on reasons and rational choice (Dietrich and List forthcoming), we describe a framework for conceptualizing preference formation and preference change. In our model, an agent's preferences are based on certain motivationally salientproperties of the alternatives over which the preferences are held. Preferences may change as new properties of the alternatives become salient or previously salient ones cease to be so. We suggest that our approach captures endogenous preferences in various contexts, and helps to illuminate the distinction between formal and substantive concepts of rationality, as well as the role of perception in rational choice.preference formation, preference change, properties, motivations, reasons, endogenous preferences, formal versus substantive rationality, perception

Moderately naturalistic metaphysics

The present paper discusses different approaches to metaphysics and defends a specific, non-deflationary approach that nevertheless qualifies as scientifically-grounded and, consequently, as acceptable from the naturalistic viewpoint. By critically assessing some recent work on science and metaphysics, we argue that such a sophisticated form of naturalism, which preserves the autonomy of metaphysics as an a priori enterprise yet pays due attention to the indications coming from our best science, is not only workable but recommended.Peer reviewe

The Mechanistic and Normative Structure of Agency

I develop an interdisciplinary framework for understanding the nature of agents and agency that is compatible with recent developments in the metaphysics of science and that also does justice to the mechanistic and normative characteristics of agents and agency as they are understood in moral philosophy, social psychology, neuroscience, robotics, and economics. The framework I develop is internal perspectivalist. That is to say, it counts agents as real in a perspective-dependent way, but not in a way that depends on an external perspective. Whether or not something counts as an agent depends on whether it is able to have a certain kind of perspective. My approach differs from many others by treating possession of a perspective as more basic than the possession of agency, representational content/vehicles, cognition, intentions, goals, concepts, or mental or psychological states; these latter capabilities require the former, not the other way around. I explain what it means for a system to be able to have a perspective at all, beginning with simple cases in biology, and show how self-contained normative perspectives about proper function and control can emerge from mechanisms with relatively simple dynamics. I then describe how increasingly complex control architectures can become organized that allow for more complex perspectives that approach agency. Next, I provide my own account of the kind of perspective that is necessary for agency itself, the goal being to provide a reference against which other accounts can be compared. Finally, I introduce a crucial distinction that is necessary for understanding human agency: that between inclinational and committal agency, and venture a hypothesis about how the normative perspective underlying committal agency might be mechanistically realized

Environcentricism: A Philosophy for a Constantly Changing World

The present disastrous predicament of flood in the world today more than ever calls for an immediate attention of every one inclusive to participate in the ongoing campaign for a more evironcentric world We live in an ever constant-changing world both for the betterment as well as the destruction of man and his world where it is either you go out and come to meet your house and property on fire or floating on a miraculous manifested ocean from a five minutes rain1 or perhaps meet your environment-house and properties being transformed by a contemporary construction technique or low cast consumption code to enhance better living By and large it is an either or universe instigating a need to adopt an environcentric philosophy worthy of connecting the disconnects and reviving our lost environmental values or valuation and obligations From an environcentric philosophical dimension The research examines the problems associated with nature or the universe and attempts answers to certain important questions as its energetic force what is the cause of this environmental disbalance how do we remedy the situation and make our universe habitable for all life forms and those of the next generation To ensure an exhaustive analysis this work shall be phenomenological and criticalanalytic in its method This study concludes with the affirmation that an environcentic philosophy which identifies and respects the deep spiritual connection between man and his environment to ensure a value and purposeful and peaceful existenc