155 research outputs found
Similarity and symmetry measures for convex sets based on Minkowski addition
This paper discusses similarity and symmetry measures for convex shapes. Their definition is based on Minkowski addition and the Brunn-Minkowski inequality. All measures considered are invariant under translations; furthermore, they may also be invariant under rotations, multiplications, reflections, or the class of all affine transformations. The examples discussed in this paper allow efficient algorithms if one restricts oneselves to convex polygons. Although it deals exclusively with the 2-dimensional case, many of the theoretical results carry over almost directly to higher-dimensional spaces. Some results obtained in this paper are illustrated by experimental data
Associahedra via spines
An associahedron is a polytope whose vertices correspond to triangulations of
a convex polygon and whose edges correspond to flips between them. Using
labeled polygons, C. Hohlweg and C. Lange constructed various realizations of
the associahedron with relevant properties related to the symmetric group and
the classical permutahedron. We introduce the spine of a triangulation as its
dual tree together with a labeling and an orientation. This notion extends the
classical understanding of the associahedron via binary trees, introduces a new
perspective on C. Hohlweg and C. Lange's construction closer to J.-L. Loday's
original approach, and sheds light upon the combinatorial and geometric
properties of the resulting realizations of the associahedron. It also leads to
noteworthy proofs which shorten and simplify previous approaches.Comment: 27 pages, 11 figures. Version 5: minor correction
VLSI Routing for Advanced Technology
Routing is a major step in VLSI design, the design process of complex integrated circuits (commonly known as chips). The basic task in routing is to connect predetermined locations on a chip (pins) with wires which serve as electrical connections. One main challenge in routing for advanced chip technology is the increasing complexity of design rules which reflect manufacturing requirements. In this thesis we investigate various aspects of this challenge. First, we consider polygon decomposition problems in the context of VLSI design rules. We introduce different width notions for polygons which are important for width-dependent design rules in VLSI routing, and we present efficient algorithms for computing width-preserving decompositions of rectilinear polygons into rectangles. Such decompositions are used in routing to allow for fast design rule checking. A main contribution of this thesis is an O(n) time algorithm for computing a decomposition of a simple rectilinear polygon with n vertices into O(n) rectangles, preseverving two-dimensional width. Here the two-dimensional width at a point of the polygon is defined as the edge length of a largest square that contains the point and is contained in the polygon. In order to obtain these results we establish a connection between such decompositions and Voronoi diagrams. Furthermore, we consider implications of multiple patterning and other advanced design rules for VLSI routing. The main contribution in this context is the detailed description of a routing approach which is able to manage such advanced design rules. As a main algorithmic concept we use multi-label shortest paths where certain path properties (which model design rules) can be enforced by defining labels assigned to path vertices and allowing only certain label transitions. The described approach has been implemented in BonnRoute, a VLSI routing tool developed at the Research Institute for Discrete Mathematics, University of Bonn, in cooperation with IBM. We present experimental results confirming that a flow combining BonnRoute and an external cleanup step produces far superior results compared to an industry standard router. In particular, our proposed flow runs more than twice as fast, reduces the via count by more than 20%, the wiring length by more than 10%, and the number of remaining design rule errors by more than 60%. These results obtained by applying our multiple patterning approach to real-world chip instances provided by IBM are another main contribution of this thesis. We note that IBM uses our proposed combined BonnRoute flow as the default tool for signal routing
Calculating the EHZ Capacity of Polytopes
In this thesis we are concerned with symplectic geometry. This rather new field of research gained much interest due to some famous results in the late 20th century, such as the celebrated non-squeezing theorem by Gromov. An intriguing feature of this theorem is, that it is true if and only if there are global symplectic invariants that satisfy certain properties. These global invariants are called symplectic capacities and their existence is a nontrivial fact. By now, several constructions are known but the computation of symplectic capacities has not received much attention. In this thesis, we address this aspect for a certain symplectic capacity, namely the Ekeland-Hofer-Zehnder capacity, which maps a nonnegative number or infinity to every convex body in . To compute the Ekeland-Hofer-Zehnder capacity of sets of the form , where both and are convex sets, we use an approach based on Minkowski Billiards. More precisely, we build on an algorithm by Alkoumi and Schlenk, that is formulated for the case where is a two-dimensional convex set and is the Euclidean unit ball. On the one hand, we adapt this algorithm to allow convex sets with arbitrary dimension. On the other hand, we generalize the approach by Alkoumi and Schlenk from the Euclidean setting (where is the Euclidean unit ball) to the Minkowski setting (where is an arbitrary convex set). In particular, we consider the case where both and are polytopes. Aside from this approach we consider a formulation of the Ekeland-Hofer-Zehnder capacity as a maximization problem, which is due to Abbondandolo and Majer. This maximization problem is a hybrid of a quadratic assignment problem and a quadratic program with non-convex objective function. We employ different optimization techniques and obtain upper and lower bounds on the Ekeland-Hofer-Zehnder capacity of polytopes. Amongst others, we obtain a very good upper bound that is equal to the exact value for many small problem instances at the cost of a rapidly increasing running time
Leaf recognition for accurate plant classification.
Doctor of Philosophy in Computer Science, University of KwaZulu-Natal, Durban 2017.Plants are the most important living organisms on our planet because they are
sources of energy and protect our planet against global warming. Botanists were
the first scientist to design techniques for plant species recognition using leaves. Although
many techniques for plant recognition using leaf images have been proposed
in the literature, the precision and the quality of feature descriptors for shape, texture,
and color remain the major challenges. This thesis investigates the precision
of geometric shape features extraction and improved the determination of the Minimum
Bounding Rectangle (MBR). The comparison of the proposed improved MBR
determination method to Chaudhuri's method is performed using Mean Absolute
Error (MAE) generated by each method on each edge point of the MBR. On the
top left point of the determined MBR, Chaudhuri's method has the MAE value of
26.37 and the proposed method has the MAE value of 8.14.
This thesis also investigates the use of the Convexity Measure of Polygons for the
characterization of the degree of convexity of a given leaf shape. Promising results
are obtained when using the Convexity Measure of Polygons combined with other
geometric features to characterize leave images, and a classification rate of 92% was
obtained with a Multilayer Perceptron Neural Network classifier. After observing
the limitations of the Convexity Measure of Polygons, a new shape feature called
Convexity Moments of Polygons is presented in this thesis. This new feature has
the invariant properties of the Convexity Measure of Polygons, but is more precise
because it uses more than one value to characterize the degree of convexity of a
given shape. Promising results are obtained when using the Convexity Moments
of Polygons combined with other geometric features to characterize the leaf images
and a classification rate of 95% was obtained with the Multilayer Perceptron Neural
Network classifier.
Leaf boundaries carry valuable information that can be used to distinguish between
plant species. In this thesis, a new boundary-based shape characterization
method called Sinuosity Coefficients is proposed. This method has been used in
many fields of science like Geography to describe rivers meandering. The Sinuosity
Coefficients is scale and translation invariant. Promising results are obtained when
using Sinuosity Coefficients combined with other geometric features to characterize
the leaf images, a classification rate of 80% was obtained with the Multilayer
Perceptron Neural Network classifier.
Finally, this thesis implements a model for plant classification using leaf images,
where an input leaf image is described using the Convexity Moments, the Sinuosity
Coefficients and the geometric features to generate a feature vector for the recognition
of plant species using a Radial Basis Neural Network. With the model designed
and implemented the overall classification rate of 97% was obtained
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