32,009 research outputs found
Genetic programming for the automatic design of controllers for a surface ship
In this paper, the implementation of genetic programming (GP) to design a contoller structure is assessed. GP is used to evolve control strategies that, given the current and desired state of the propulsion and heading dynamics of a supply ship as inputs, generate the command forces required to maneuver the ship. The controllers created using GP are evaluated through computer simulations and real maneuverability tests in a laboratory water basin facility. The robustness of each controller is analyzed through the simulation of environmental disturbances. In addition, GP runs in the presence of disturbances are carried out so that the different controllers obtained can be compared. The particular vessel used in this paper is a scale model of a supply ship called CyberShip II. The results obtained illustrate the benefits of using GP for the automatic design of propulsion and navigation controllers for surface ships
Convergence of Fuzzy Tori and Quantum Tori for the quantum Gromov-Hausdorff Propinquity: an explicit approach
Quantum tori are limits of finite dimensional C*-algebras for the quantum
Gromov-Hausdorff propinquity, a metric defined by the author as a strengthening
of Rieffel's quantum Gromov-Hausdorff designed to retain the C*-algebraic
structure. In this paper, we propose a proof of the continuity of the family of
quantum and fuzzy tori which relies on explicit representations of the
C*-algebras rather than on more abstract arguments, in a manner which takes
full advantage of the notion of bridge defining the quantum propinquity.Comment: 41 Pages. This paper is the second half of ArXiv:1302.4058v2. The
latter paper has been divided in two halves for publications purposes, with
the first half now the current version of 1302.4058, which has been accepted
in Trans. Amer. Math. Soc. This second half is now a stand-alone paper, with
a brief summary of 1302.4058 and a new introductio
Affine Registration of label maps in Label Space
Two key aspects of coupled multi-object shape\ud
analysis and atlas generation are the choice of representation\ud
and subsequent registration methods used to align the sample\ud
set. For example, a typical brain image can be labeled into\ud
three structures: grey matter, white matter and cerebrospinal\ud
fluid. Many manipulations such as interpolation, transformation,\ud
smoothing, or registration need to be performed on these images\ud
before they can be used in further analysis. Current techniques\ud
for such analysis tend to trade off performance between the two\ud
tasks, performing well for one task but developing problems when\ud
used for the other.\ud
This article proposes to use a representation that is both\ud
flexible and well suited for both tasks. We propose to map object\ud
labels to vertices of a regular simplex, e.g. the unit interval for\ud
two labels, a triangle for three labels, a tetrahedron for four\ud
labels, etc. This representation, which is routinely used in fuzzy\ud
classification, is ideally suited for representing and registering\ud
multiple shapes. On closer examination, this representation\ud
reveals several desirable properties: algebraic operations may\ud
be done directly, label uncertainty is expressed as a weighted\ud
mixture of labels (probabilistic interpretation), interpolation is\ud
unbiased toward any label or the background, and registration\ud
may be performed directly.\ud
We demonstrate these properties by using label space in a gradient\ud
descent based registration scheme to obtain a probabilistic\ud
atlas. While straightforward, this iterative method is very slow,\ud
could get stuck in local minima, and depends heavily on the initial\ud
conditions. To address these issues, two fast methods are proposed\ud
which serve as coarse registration schemes following which the\ud
iterative descent method can be used to refine the results. Further,\ud
we derive an analytical formulation for direct computation of the\ud
"group mean" from the parameters of pairwise registration of all\ud
the images in the sample set. We show results on richly labeled\ud
2D and 3D data sets
Trefftz Difference Schemes on Irregular Stencils
The recently developed Flexible Local Approximation MEthod (FLAME) produces
accurate difference schemes by replacing the usual Taylor expansion with
Trefftz functions -- local solutions of the underlying differential equation.
This paper advances and casts in a general form a significant modification of
FLAME proposed recently by Pinheiro & Webb: a least-squares fit instead of the
exact match of the approximate solution at the stencil nodes. As a consequence
of that, FLAME schemes can now be generated on irregular stencils with the
number of nodes substantially greater than the number of approximating
functions. The accuracy of the method is preserved but its robustness is
improved. For demonstration, the paper presents a number of numerical examples
in 2D and 3D: electrostatic (magnetostatic) particle interactions, scattering
of electromagnetic (acoustic) waves, and wave propagation in a photonic
crystal. The examples explore the role of the grid and stencil size, of the
number of approximating functions, and of the irregularity of the stencils.Comment: 28 pages, 12 figures; to be published in J Comp Phy
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