2,311 research outputs found
End-to-end Sampling Patterns
Sample patterns have many uses in Computer Graphics, ranging from procedural
object placement over Monte Carlo image synthesis to non-photorealistic
depiction. Their properties such as discrepancy, spectra, anisotropy, or
progressiveness have been analyzed extensively. However, designing methods to
produce sampling patterns with certain properties can require substantial
hand-crafting effort, both in coding, mathematical derivation and compute time.
In particular, there is no systematic way to derive the best sampling algorithm
for a specific end-task.
Tackling this issue, we suggest another level of abstraction: a toolkit to
end-to-end optimize over all sampling methods to find the one producing
user-prescribed properties such as discrepancy or a spectrum that best fit the
end-task. A user simply implements the forward losses and the sampling method
is found automatically -- without coding or mathematical derivation -- by
making use of back-propagation abilities of modern deep learning frameworks.
While this optimization takes long, at deployment time the sampling method is
quick to execute as iterated unstructured non-linear filtering using radial
basis functions (RBFs) to represent high-dimensional kernels. Several important
previous methods are special cases of this approach, which we compare to
previous work and demonstrate its usefulness in several typical Computer
Graphics applications. Finally, we propose sampling patterns with properties
not shown before, such as high-dimensional blue noise with projective
properties
Projections of determinantal point processes
Let be a space filling-design of
points defined in . In computer experiments, an important property
seeked for is a nice coverage of . This property could
be desirable as well as for any projection of onto
for . Thus we expect that , which represents the design
with coordinates associated to any index set , remains
regular in where is the cardinality of . This paper
examines the conservation of nice coverage by projection using spatial point
processes, and more specifically using the class of determinantal point
processes. We provide necessary conditions on the kernel defining these
processes, ensuring that the projected point process is
repulsive, in the sense that its pair correlation function is uniformly bounded
by 1, for all . We present a few examples, compare
them using a new normalized version of Ripley's function. Finally, we
illustrate the interest of this research for Monte-Carlo integration
Evolution of galaxies due to self-excitation
These lectures will cover methods for studying the evolution of galaxies
since their formation. Because the properties of a galaxy depend on its
history, an understanding of galaxy evolution requires that we understand the
dynamical interplay between all components. The first part will emphasize
n-body simulation methods which minimize sampling noise. These techniques are
based on harmonic expansions and scale linearly with the number of bodies,
similar to Fourier transform solutions used in cosmological simulations.
Although fast, until recently they were only efficiently used for small number
of geometries and background profiles. These same techniques may be used to
study the modes and response of a galaxy to an arbitrary perturbation. In
particular, I will describe the modal spectra of stellar systems and role of
damped modes which are generic to stellar systems in interactions and appear to
play a significant role in determining the common structures that we see. The
general development leads indirectly to guidelines for the number of particles
necessary to adequately represent the gravitational field such that the modal
spectrum is resolvable. I will then apply these same excitation to
understanding the importance of noise to galaxy evolution.Comment: 24 pages, 7 figures, using Sussp.sty (included). Lectures presented
at the NATO Advanced Study Institute, "The Restless Universe: Applications of
Gravitational N-Body Dynamics to Planetary, Stellar and Galactic Systems,"
Blair Atholl, July 200
Objective Classification of Galaxy Spectra using the Information Bottleneck Method
A new method for classification of galaxy spectra is presented, based on a
recently introduced information theoretical principle, the `Information
Bottleneck'. For any desired number of classes, galaxies are classified such
that the information content about the spectra is maximally preserved. The
result is classes of galaxies with similar spectra, where the similarity is
determined via a measure of information. We apply our method to approximately
6000 galaxy spectra from the ongoing 2dF redshift survey, and a mock-2dF
catalogue produced by a Cold Dark Matter-based semi-analytic model of galaxy
formation. We find a good match between the mean spectra of the classes found
in the data and in the models. For the mock catalogue, we find that the classes
produced by our algorithm form an intuitively sensible sequence in terms of
physical properties such as colour, star formation activity, morphology, and
internal velocity dispersion. We also show the correlation of the classes with
the projections resulting from a Principal Component Analysis.Comment: submitted to MNRAS, 17 pages, Latex, with 14 figures embedde
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