58,078 research outputs found
On the Minimal Revision Problem of Specification Automata
As robots are being integrated into our daily lives, it becomes necessary to
provide guarantees on the safe and provably correct operation. Such guarantees
can be provided using automata theoretic task and mission planning where the
requirements are expressed as temporal logic specifications. However, in
real-life scenarios, it is to be expected that not all user task requirements
can be realized by the robot. In such cases, the robot must provide feedback to
the user on why it cannot accomplish a given task. Moreover, the robot should
indicate what tasks it can accomplish which are as "close" as possible to the
initial user intent. This paper establishes that the latter problem, which is
referred to as the minimal specification revision problem, is NP complete. A
heuristic algorithm is presented that can compute good approximations to the
Minimal Revision Problem (MRP) in polynomial time. The experimental study of
the algorithm demonstrates that in most problem instances the heuristic
algorithm actually returns the optimal solution. Finally, some cases where the
algorithm does not return the optimal solution are presented.Comment: 23 pages, 16 figures, 2 tables, International Joural of Robotics
Research 2014 Major Revision (submitted
A Counting Logic for Structure Transition Systems
Quantitative questions such as "what is the maximum number of tokens
in a place of a Petri net?" or "what is the maximal reachable height
of the stack of a pushdown automaton?" play a significant role in
understanding models of computation. To study such problems in a
systematic way, we introduce structure transition systems on which
one can define logics that mix temporal expressions (e.g. reachability) with properties of a state (e.g. the height of the stack). We propose a counting logic Qmu[#MSO] which allows to express questions like the ones above, and also many boundedness problems studied so far. We show that Qmu[#MSO] has good algorithmic properties, in particular we generalize two standard methods in model checking, decomposition on trees and model checking through parity games, to this quantitative logic. These properties are used to prove decidability of Qmu[#MSO] on tree-producing pushdown systems, a generalization of both pushdown systems and regular tree grammars
Visualization in spatial modeling
This chapter deals with issues arising from a central theme in contemporary computer modeling - visualization. We first tie visualization to varieties of modeling along the continuum from iconic to symbolic and then focus on the notion that our models are so intrinsically complex that there are many different types of visualization that might be developed in their understanding and implementation. This focuses the debate on the very way of 'doing science' in that patterns and processes of any complexity can be better understood through visualizing the data, the simulations, and the outcomes that such models generate. As we have grown more sensitive to the problem of complexity in all systems, we are more aware that the twin goals of parsimony and verifiability which have dominated scientific theory since the 'Enlightenment' are up for grabs: good theories and models must 'look right' despite what our statistics and causal logics tell us. Visualization is the cutting edge of this new way of thinking about science but its styles vary enormously with context. Here we define three varieties: visualization of complicated systems to make things simple or at least explicable, which is the role of pedagogy; visualization to explore unanticipated outcomes and to refine processes that interact in unanticipated ways; and visualization to enable end users with no prior understanding of the science but a deep understanding of the problem to engage in using models for prediction, prescription, and control. We illustrate these themes with a model of an agricultural market which is the basis of modern urban economics - the von Thünen model of land rent and density; a model of urban development based on interacting spatial and temporal processes of land development - the DUEM model; and a pedestrian model of human movement at the fine scale where control of such movements to meet standards of public safety is intrinsically part of the model about which the controllers know intimately. © Springer-Verlag Berlin Heidelberg 2006
A stable environment: surrogacy and the good life in Scotland
In this thesis I describe the claims that a group of people living in rural
Scotland make about maternal surrogacy. For them, surrogacy is a topical issue
that provokes speculative ethical judgements. This is in a context in which they
are building good lives, strongly informed by environmentalist �ethical living� and
local wildlife conservation. I describe the kinds of ideas they employ and
reproduce in discussing the ethics of surrogacy to capture the nuanced
judgements that go into ethical claim-making. I argue that, in order to
understand these people�s ideas about what is natural and what is moral, they
should be considered along with their more ordinary ideas and practices. I
describe how some of the same concepts they use to talk about surrogacy
figure in their conceptions of goodness and what makes a good life, in order to
both contextualise and extend their ideas about the ethics of surrogacy.
Through ethnography of their everyday lives, I show the importance of
effort and care in the making of relationships with other people, animals and the
land and in fashioning an ethical subjectivity. I analyse the connections between
nature, kinship and ethics in lives that are structured by efforts to protect the
natural world, feel closer to other people and experience a fulfilling life. I
examine the importance of choice and money in enabling these lives and raise
questions about the location and status of transcendent values in contemporary
Britain. I discuss the temporal orientation of these people in relation to the
influence of environmentalist ideas of impending ecological crisis and consider
how this links with their ideas about how to live in the present as well as how
these connect up with their ideas about parenthood and kinship
Bayesian Probabilities and the Histories Algebra
We attempt a justification of a generalisation of the consistent histories
programme using a notion of probability that is valid for all complete sets of
history propositions. This consists of introducing Cox's axioms of probability
theory and showing that our candidate notion of probability obeys them. We also
give a generalisation of Bayes' theorem and comment upon how Bayesianism should
be useful for the quantum gravity/cosmology programmes.Comment: 10 pages, accepted by Int. J. Theo. Phys. Feb 200
Two-Way Unary Temporal Logic over Trees
We consider a temporal logic EF+F^-1 for unranked, unordered finite trees.
The logic has two operators: EF\phi, which says "in some proper descendant \phi
holds", and F^-1\phi, which says "in some proper ancestor \phi holds". We
present an algorithm for deciding if a regular language of unranked finite
trees can be expressed in EF+F^-1. The algorithm uses a characterization
expressed in terms of forest algebras.Comment: 29 pages. Journal version of a LICS 07 pape
- …