90,196 research outputs found
Practical Model-Based Diagnosis with Qualitative Possibilistic Uncertainty
An approach to fault isolation that exploits vastly incomplete models is
presented. It relies on separate descriptions of each component behavior,
together with the links between them, which enables focusing of the reasoning
to the relevant part of the system. As normal observations do not need
explanation, the behavior of the components is limited to anomaly propagation.
Diagnostic solutions are disorders (fault modes or abnormal signatures) that
are consistent with the observations, as well as abductive explanations. An
ordinal representation of uncertainty based on possibility theory provides a
simple exception-tolerant description of the component behaviors. We can for
instance distinguish between effects that are more or less certainly present
(or absent) and effects that are more or less certainly present (or absent)
when a given anomaly is present. A realistic example illustrates the benefits
of this approach.Comment: Appears in Proceedings of the Eleventh Conference on Uncertainty in
Artificial Intelligence (UAI1995
Efficient resolution of the Colebrook equation
A robust, fast and accurate method for solving the Colebrook-like equations
is presented. The algorithm is efficient for the whole range of parameters
involved in the Colebrook equation. The computations are not more demanding
than simplified approximations, but they are much more accurate. The algorithm
is also faster and more robust than the Colebrook solution expressed in term of
the Lambert W-function. Matlab and FORTRAN codes are provided
On semidefinite representations of plane quartics
This note focuses on the problem of representing convex sets as projections
of the cone of positive semidefinite matrices, in the particular case of sets
generated by bivariate polynomials of degree four. Conditions are given for the
convex hull of a plane quartic to be exactly semidefinite representable with at
most 12 lifting variables. If the quartic is rationally parametrizable, an
exact semidefinite representation with 2 lifting variables can be obtained.
Various numerical examples illustrate the techniques and suggest further
research directions
Non linear eigenvalue problems
In this paper we consider generalized eigenvalue problems for a family of
operators with a polynomial dependence on a complex parameter. This problem is
equivalent to a genuine non self-adjoint operator. We discuss here existence of
non trivial eigenstates for models coming from analytic theory of smoothness
for P.D.E. We shall review some old results and present recent improvements on
this subject
Time Evolution of States for Open Quantum Systems. The quadratic case
Our main goal in this paper is to extend to any system of coupled quadratic
Hamiltonians some properties known for systems of quantum harmonic oscillators
related with the Brownian Quantum Motion model. In a first part we get a rather
general formula for the purity (or the linear entropy) in a short time
approximation. In a second part we establish a master equation (or a
Fokker-Planck type equation) for the time evolution of the reduced matrix
density for bilinearly coupled quadratic Hamiltonians.
The Hamiltonians and the bilinear coupling can be time dependent.
Moreover we give an explicit formula for the solution of this master equation
so that the time evolution of the reduced density at time is connected with
the reduced density at initial time for where
is a critical time but reversibility is lost for
Lisp, Jazz, Aikido -- Three Expressions of a Single Essence
The relation between Science (what we can explain) and Art (what we can't)
has long been acknowledged and while every science contains an artistic part,
every art form also needs a bit of science. Among all scientific disciplines,
programming holds a special place for two reasons. First, the artistic part is
not only undeniable but also essential. Second, and much like in a purely
artistic discipline, the act of programming is driven partly by the notion of
aesthetics: the pleasure we have in creating beautiful things. Even though the
importance of aesthetics in the act of programming is now unquestioned, more
could still be written on the subject. The field called "psychology of
programming" focuses on the cognitive aspects of the activity, with the goal of
improving the productivity of programmers. While many scientists have
emphasized their concern for aesthetics and the impact it has on their
activity, few computer scientists have actually written about their thought
process while programming. What makes us like or dislike such and such language
or paradigm? Why do we shape our programs the way we do? By answering these
questions from the angle of aesthetics, we may be able to shed some new light
on the art of programming. Starting from the assumption that aesthetics is an
inherently transversal dimension, it should be possible for every programmer to
find the same aesthetic driving force in every creative activity they
undertake, not just programming, and in doing so, get deeper insight on why and
how they do things the way they do. On the other hand, because our aesthetic
sensitivities are so personal, all we can really do is relate our own
experiences and share it with others, in the hope that it will inspire them to
do the same. My personal life has been revolving around three major creative
activities, of equal importance: programming in Lisp, playing Jazz music, and
practicing Aikido. But why so many of them, why so different ones, and why
these specifically? By introspecting my personal aesthetic sensitivities, I
eventually realized that my tastes in the scientific, artistic, and physical
domains are all motivated by the same driving forces, hence unifying Lisp,
Jazz, and Aikido as three expressions of a single essence, not so different
after all. Lisp, Jazz, and Aikido are governed by a limited set of rules which
remain simple and unobtrusive. Conforming to them is a pleasure. Because Lisp,
Jazz, and Aikido are inherently introspective disciplines, they also invite you
to transgress the rules in order to find your own. Breaking the rules is fun.
Finally, if Lisp, Jazz, and Aikido unify so many paradigms, styles, or
techniques, it is not by mere accumulation but because they live at the
meta-level and let you reinvent them. Working at the meta-level is an
enlightening experience. Understand your aesthetic sensitivities and you may
gain considerable insight on your own psychology of programming. Mine is
perhaps common to most lispers. Perhaps also common to other programming
communities, but that, is for the reader to decide..
On convexity of the frequency response of a stable polynomial
In the complex plane, the frequency response of a univariate polynomial is
the set of values taken by the polynomial when evaluated along the imaginary
axis. This is an algebraic curve partitioning the plane into several connected
components. In this note it is shown that the component including the origin is
exactly representable by a linear matrix inequality if and only if the
polynomial is stable, in the sense that all its roots have negative real parts
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