15,439 research outputs found
Feasible approach for the computer implementation of parametric visual calculating
Thesis (S.M. in Architecture Studies)--Massachusetts Institute of Technology, Dept. of Architecture, 2013.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (p. 62-66).Computational design tools in architecture currently fall into two broad categories: Tools for representation and tools for generative design, including scripting. However, both categories address only relatively methodical aspects of designing, and do little to support the design freedom and serendipitous creativity that, for example, is afforded by iterative sketching. Calculating with visual rules provides an explicit notation for such artistic processes of seeing and drawing. Shape grammars have validated this approach by formalizing many existing designs and styles as visual rule-sets. In this way, visual rules store and transfer design knowledge. Visual calculating in a more general sense supports creativity by allowing a designer to apply any rule she wants, and to capriciously see and re-see the design. In contrast to other explicit design methodologies, visual calculating defines a decomposition into parts only after the design is calculated, thus allowing formalization without impeding design freedom. Located at the intersection between design and computation, the computer implementation of visual calculating presents an opportunity for more designerly computational design tools. Since parametric visual calculating affords the largest set of design possibilities, the computer implementation of parametric visual calculating will allow flexible, rule-based design tools that intelligently combine design freedom with computational processing power. In order to compute with shapes, a symbolic representation for shapes is necessary. This thesis examines several symbolic representations for shapes, including graphs. Especially close attention is given to graph-based representations, since graphs are well suited to represent parametric shapes. Based on this analysis, this thesis proposes a new graph for parametric shapes that is clearer, more compact and closer the original formulation of visual calculating than existing approaches, while also strongly supporting design freedom. The thesis provides algorithms and heuristics to construct this "inverted" graph, for connected and unconnected shapes.by Thomas Alois Wortmann.S.M.in Architecture Studie
Non-Markovian Monte Carlo Algorithm for the Constrained Markovian Evolution in QCD
We revisit the challenging problem of finding an efficient Monte Carlo (MC)
algorithm solving the constrained evolution equations for the initial-state QCD
radiation. The type of the parton (quark, gluon) and the energy fraction x of
the parton exiting emission chain (entering hard process) are predefined, i.e.
constrained throughout the evolution. Such a constraint is mandatory for any
realistic MC for the initial state QCD parton shower. We add one important
condition: the MC algorithm must not require the a priori knowledge of the full
numerical exact solutions of the evolution equations, as is the case in the
popular ``Markovian MC for backward evolution''. Our aim is to find at least
one solution of this problem that would function in practice. Finding such a
solution seems to be definitely within the reach of the currently available
computer CPUs and the sophistication of the modern MC techniques. We describe
in this work the first example of an efficient solution of this kind. Its
numerical implementation is still restricted to the pure gluon-strahlung. As
expected, it is not in the class of the so-called Markovian MCs. For this
reason we refer to it as belonging to a class of non-Markovian MCs. We show
that numerical results of our new MC algorithm agree very well (to 0.2%) with
the results of the other MC program of our own (unconstrained Markovian) and
another non-MC program QCDnum16. This provides a proof of the existence of the
new class of MC techniques, to be exploited in the precision perturbative QCD
calculations for the Large Hadron Collider
An Arbitrary Curvilinear Coordinate Method for Particle-In-Cell Modeling
A new approach to the kinetic simulation of plasmas in complex geometries,
based on the Particle-in- Cell (PIC) simulation method, is explored. In the two
dimensional (2d) electrostatic version of our method, called the Arbitrary
Curvilinear Coordinate PIC (ACC-PIC) method, all essential PIC operations are
carried out in 2d on a uniform grid on the unit square logical domain, and
mapped to a nonuniform boundary-fitted grid on the physical domain. As the
resulting logical grid equations of motion are not separable, we have developed
an extension of the semi-implicit Modified Leapfrog (ML) integration technique
to preserve the symplectic nature of the logical grid particle mover. A
generalized, curvilinear coordinate formulation of Poisson's equations to solve
for the electrostatic fields on the uniform logical grid is also developed. By
our formulation, we compute the plasma charge density on the logical grid based
on the particles' positions on the logical domain. That is, the plasma
particles are weighted to the uniform logical grid and the self-consistent mean
electrostatic fields obtained from the solution of the logical grid Poisson
equation are interpolated to the particle positions on the logical grid. This
process eliminates the complexity associated with the weighting and
interpolation processes on the nonuniform physical grid and allows us to run
the PIC method on arbitrary boundary-fitted meshes.Comment: Submitted to Computational Science & Discovery December 201
A numerical algorithm for semi-discrete optimal transport in 3D
This paper introduces a numerical algorithm to compute the optimal
transport map between two measures and , where derives from a
density defined as a piecewise linear function (supported by a
tetrahedral mesh), and where is a sum of Dirac masses.
I first give an elementary presentation of some known results on optimal
transport and then observe a relation with another problem (optimal sampling).
This relation gives simple arguments to study the objective functions that
characterize both problems.
I then propose a practical algorithm to compute the optimal transport map
between a piecewise linear density and a sum of Dirac masses in 3D. In this
semi-discrete setting, Aurenhammer et.al [\emph{8th Symposium on Computational
Geometry conf. proc.}, ACM (1992)] showed that the optimal transport map is
determined by the weights of a power diagram. The optimal weights are computed
by minimizing a convex objective function with a quasi-Newton method. To
evaluate the value and gradient of this objective function, I propose an
efficient and robust algorithm, that computes at each iteration the
intersection between a power diagram and the tetrahedral mesh that defines the
measure .
The numerical algorithm is experimented and evaluated on several datasets,
with up to hundred thousands tetrahedra and one million Dirac masses.Comment: 23 pages, 14 figure
Risk-sensitive Inverse Reinforcement Learning via Semi- and Non-Parametric Methods
The literature on Inverse Reinforcement Learning (IRL) typically assumes that
humans take actions in order to minimize the expected value of a cost function,
i.e., that humans are risk neutral. Yet, in practice, humans are often far from
being risk neutral. To fill this gap, the objective of this paper is to devise
a framework for risk-sensitive IRL in order to explicitly account for a human's
risk sensitivity. To this end, we propose a flexible class of models based on
coherent risk measures, which allow us to capture an entire spectrum of risk
preferences from risk-neutral to worst-case. We propose efficient
non-parametric algorithms based on linear programming and semi-parametric
algorithms based on maximum likelihood for inferring a human's underlying risk
measure and cost function for a rich class of static and dynamic
decision-making settings. The resulting approach is demonstrated on a simulated
driving game with ten human participants. Our method is able to infer and mimic
a wide range of qualitatively different driving styles from highly risk-averse
to risk-neutral in a data-efficient manner. Moreover, comparisons of the
Risk-Sensitive (RS) IRL approach with a risk-neutral model show that the RS-IRL
framework more accurately captures observed participant behavior both
qualitatively and quantitatively, especially in scenarios where catastrophic
outcomes such as collisions can occur.Comment: Submitted to International Journal of Robotics Research; Revision 1:
(i) Clarified minor technical points; (ii) Revised proof for Theorem 3 to
hold under weaker assumptions; (iii) Added additional figures and expanded
discussions to improve readabilit
Notions of optimal transport theory and how to implement them on a computer
This article gives an introduction to optimal transport, a mathematical
theory that makes it possible to measure distances between functions (or
distances between more general objects), to interpolate between objects or to
enforce mass/volume conservation in certain computational physics simulations.
Optimal transport is a rich scientific domain, with active research
communities, both on its theoretical aspects and on more applicative
considerations, such as geometry processing and machine learning. This article
aims at explaining the main principles behind the theory of optimal transport,
introduce the different involved notions, and more importantly, how they
relate, to let the reader grasp an intuition of the elegant theory that
structures them. Then we will consider a specific setting, called
semi-discrete, where a continuous function is transported to a discrete sum of
Dirac masses. Studying this specific setting naturally leads to an efficient
computational algorithm, that uses classical notions of computational geometry,
such as a generalization of Voronoi diagrams called Laguerre diagrams.Comment: 32 pages, 17 figure
Hyperuniformity of Quasicrystals
Hyperuniform systems, which include crystals, quasicrystals and special
disordered systems, have attracted considerable recent attention, but rigorous
analyses of the hyperuniformity of quasicrystals have been lacking because the
support of the spectral intensity is dense and discontinuous. We employ the
integrated spectral intensity, , to quantitatively characterize the
hyperuniformity of quasicrystalline point sets generated by projection methods.
The scaling of as tends to zero is computed for one-dimensional
quasicrystals and shown to be consistent with independent calculations of the
variance, , in the number of points contained in an interval of
length . We find that one-dimensional quasicrystals produced by projection
from a two-dimensional lattice onto a line of slope fall into distinct
classes determined by the width of the projection window. For a countable dense
set of widths, ; for all others, . This
distinction suggests that measures of hyperuniformity define new classes of
quasicrystals in higher dimensions as well.Comment: 12 pages, 14 figure
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