21,066 research outputs found
On the noncommutative geometry of tilings
This is a chapter in an incoming book on aperiodic order. We review results
about the topology, the dynamics, and the combinatorics of aperiodically
ordered tilings obtained with the tools of noncommutative geometry
Computing a Compact Spline Representation of the Medial Axis Transform of a 2D Shape
We present a full pipeline for computing the medial axis transform of an
arbitrary 2D shape. The instability of the medial axis transform is overcome by
a pruning algorithm guided by a user-defined Hausdorff distance threshold. The
stable medial axis transform is then approximated by spline curves in 3D to
produce a smooth and compact representation. These spline curves are computed
by minimizing the approximation error between the input shape and the shape
represented by the medial axis transform. Our results on various 2D shapes
suggest that our method is practical and effective, and yields faithful and
compact representations of medial axis transforms of 2D shapes.Comment: GMP14 (Geometric Modeling and Processing
Numerics and Fractals
Local iterated function systems are an important generalisation of the
standard (global) iterated function systems (IFSs). For a particular class of
mappings, their fixed points are the graphs of local fractal functions and
these functions themselves are known to be the fixed points of an associated
Read-Bajactarevi\'c operator. This paper establishes existence and properties
of local fractal functions and discusses how they are computed. In particular,
it is shown that piecewise polynomials are a special case of local fractal
functions. Finally, we develop a method to compute the components of a local
IFS from data or (partial differential) equations.Comment: version 2: minor updates and section 6.1 rewritten, arXiv admin note:
substantial text overlap with arXiv:1309.0243. text overlap with
arXiv:1309.024
Partial regularity and smooth topology-preserving approximations of rough domains
For a bounded domain of class ,
the properties are studied of fields of `good directions', that is the
directions with respect to which can be locally represented as
the graph of a continuous function. For any such domain there is a canonical
smooth field of good directions defined in a suitable neighbourhood of
, in terms of which a corresponding flow can be defined. Using
this flow it is shown that can be approximated from the inside and the
outside by diffeomorphic domains of class . Whether or not the image
of a general continuous field of good directions (pseudonormals) defined on
is the whole of is shown to depend on the
topology of . These considerations are used to prove that if ,
or if has nonzero Euler characteristic, there is a point
in the neighbourhood of which is
Lipschitz. The results provide new information even for more regular domains,
with Lipschitz or smooth boundaries.Comment: Final version appeared in Calc. Var PDE 56, Issue 1, 201
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