700 research outputs found
Research in interactive scene analysis
Cooperative (man-machine) scene analysis techniques were developed whereby humans can provide a computer with guidance when completely automated processing is infeasible. An interactive approach promises significant near-term payoffs in analyzing various types of high volume satellite imagery, as well as vehicle-based imagery used in robot planetary exploration. This report summarizes the work accomplished over the duration of the project and describes in detail three major accomplishments: (1) the interactive design of texture classifiers; (2) a new approach for integrating the segmentation and interpretation phases of scene analysis; and (3) the application of interactive scene analysis techniques to cartography
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Applications of lattice theory to model checking
textSociety is increasingly dependent on the correct operation of concurrent and distributed software systems. Examples of such systems include computer networks, operating systems, telephone switches and flight control systems. Model checking is a useful tool for ensuring the correctness of such systems, because it is a fully automatic technique whose use does not require expert knowledge. Additionally, model checking allows for the production of error trails when a violation of a desired property is detected. Error trails are an invaluable debugging aid, because they provide the programmer with the sequence of events that lead to an error. Model checking typically operates by performing an exhaustive exploration of the state space of the program. Exhaustive state space exploration is not practical for industrial use in the verification of concurrent systems because of the well-known phenomenon of state space explosion caused by the exploration of all possible interleavings of concurrent events. However, the exploration of all possible interleavings is not always necessary for verification. In this dissertation, we show that results from lattice theory can be applied to ameliorate state space explosion due to concurrency, and to produce short error trails when an error is detected. We show that many CTL formulae exhibit lattice-theoretic structure that can be exploited to avoid exploring multiple interleavings of a set of concurrent events. We use this structural information to develop efficient model checking techniques for both implicit (partial order) and explicit (interleaving) models of the state space. For formulae that do not exhibit the required structure, we present a technique called predicate filtering, which uses a weaker property with the desired structural characteristics to obtain a reduced state space which can then be exhaustively explored. We also show that lattice theory can be used to obtain a path of shortest length to an error state, thereby producing short error trails that greatly ease the task of debugging. We provide experimental results from a wide range of examples, showing the effectiveness of our techniques at improving the efficiency of verifying and debugging concurrent and distributed systems. Our implementation is based on the popular model checker SPIN, and we compare our performance against the state-of-the-art state space reduction strategies implemented in SPIN.Electrical and Computer Engineerin
On the logic of theory change: contraction without recovery
The postulate of Recovery, among the six postulates for theory contraction, formulated
and studied by Alchourron, G ´ ardenfors and Makinson is the one that has provoked most controversy. ¨
In this article we construct withdrawal functions that do not satisfy Recovery, but try to preserve
minimal change, and relate these withdrawal functions with the AGM contraction functions.info:eu-repo/semantics/publishedVersio
On Sparse Representation in Fourier and Local Bases
We consider the classical problem of finding the sparse representation of a
signal in a pair of bases. When both bases are orthogonal, it is known that the
sparse representation is unique when the sparsity of the signal satisfies
, where is the mutual coherence of the dictionary.
Furthermore, the sparse representation can be obtained in polynomial time by
Basis Pursuit (BP), when . Therefore, there is a gap between the
unicity condition and the one required to use the polynomial-complexity BP
formulation. For the case of general dictionaries, it is also well known that
finding the sparse representation under the only constraint of unicity is
NP-hard.
In this paper, we introduce, for the case of Fourier and canonical bases, a
polynomial complexity algorithm that finds all the possible -sparse
representations of a signal under the weaker condition that . Consequently, when , the proposed algorithm solves the
unique sparse representation problem for this structured dictionary in
polynomial time. We further show that the same method can be extended to many
other pairs of bases, one of which must have local atoms. Examples include the
union of Fourier and local Fourier bases, the union of discrete cosine
transform and canonical bases, and the union of random Gaussian and canonical
bases
Kernel Bayes' rule
A nonparametric kernel-based method for realizing Bayes' rule is proposed,
based on representations of probabilities in reproducing kernel Hilbert spaces.
Probabilities are uniquely characterized by the mean of the canonical map to
the RKHS. The prior and conditional probabilities are expressed in terms of
RKHS functions of an empirical sample: no explicit parametric model is needed
for these quantities. The posterior is likewise an RKHS mean of a weighted
sample. The estimator for the expectation of a function of the posterior is
derived, and rates of consistency are shown. Some representative applications
of the kernel Bayes' rule are presented, including Baysian computation without
likelihood and filtering with a nonparametric state-space model.Comment: 27 pages, 5 figure
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