8 research outputs found
Embedding Graphs into Embedded Graphs
A (possibly degenerate) drawing of a graph G in the plane is approximable by an embedding if it can be turned into an embedding by an arbitrarily small perturbation.
We show that testing, whether a drawing of a planar graph G in the plane is approximable by an embedding, can be carried out in polynomial time, if a desired embedding of G belongs to a fixed isotopy class, i.e., the rotation system (or equivalently the faces) of the embedding of G and the choice of outer face are fixed.
In other words, we show that c-planarity with embedded pipes is tractable for graphs with fixed embeddings.
To the best of our knowledge an analogous result was previously known essentially only when G is a cycle
Constrained Planarity in Practice -- Engineering the Synchronized Planarity Algorithm
In the constrained planarity setting, we ask whether a graph admits a planar
drawing that additionally satisfies a given set of constraints. These
constraints are often derived from very natural problems; prominent examples
are Level Planarity, where vertices have to lie on given horizontal lines
indicating a hierarchy, and Clustered Planarity, where we additionally draw the
boundaries of clusters which recursively group the vertices in a crossing-free
manner. Despite receiving significant amount of attention and substantial
theoretical progress on these problems, only very few of the found solutions
have been put into practice and evaluated experimentally.
In this paper, we describe our implementation of the recent quadratic-time
algorithm by Bl\"asius et al. [TALG Vol 19, No 4] for solving the problem
Synchronized Planarity, which can be seen as a common generalization of several
constrained planarity problems, including the aforementioned ones. Our
experimental evaluation on an existing benchmark set shows that even our
baseline implementation outperforms all competitors by at least an order of
magnitude. We systematically investigate the degrees of freedom in the
implementation of the Synchronized Planarity algorithm for larger instances and
propose several modifications that further improve the performance. Altogether,
this allows us to solve instances with up to 100 vertices in milliseconds and
instances with up to 100 000 vertices within a few minutes.Comment: to appear in Proceedings of ALENEX 202
Outerplanar partial cubes
Treballs Finals de Grau de MatemĂ tiques, Facultat de MatemĂ tiques, Universitat de Barcelona, Any: 2022, Director: Kolja Knauer[en] The class of outerplanar graphs is minor-closed and can be characterized by two excluded minors: and Partial cubes are a class of graphs with good metric properties and have two defined operations that transform a partial cube into a PC-minor. We will study the outerplanar partial cubes, which is a PC-minor-closed class. The main result is the characterization of the set of obstructions of the class of outerplanar partial cubes
Real-time interactive visualization of large networks on a tiled display system
This paper introduces a methodology for visualizing large real-world (social) network data on a high-resolution tiled display system. Advances in network drawing algorithms enabled real-time visualization and interactive exploration of large real-world networks. However, visualization on a typical desktop monitor remains challenging due to the limited amount of screen space and ever increasing size of real-world datasets.To solve this problem, we propose an integrated approach that employs state-of-the-art network visual-ization algorithms on a tiled display system consisting of multiple screens. Key to our approach is to use the machine's graphics processing units (GPUs) to their fullest extent, in order to ensure an interactive setting with real-time visualization. To realize this, we extended a recent GPU-based implementation of a force-directed graph layout algorithm to multiple GPUs and combined this with a distributed rendering approach in which each graphics card in the tiled display system renders precisely the part of the network to be displayed on the monitors attached to it.Our evaluation of the approach on a 12-screen 25 megapixels tiled display system with three GPUs, demonstrates interactive performance at 60 frames per second for real-world networks with tens of thousands of nodes and edges. This constitutes a performance improvement of approximately 4 times over a single GPU implementation. All the software developed to implement our tiled visualization approach, including the multi-GPU network layout, rendering, display and interaction components, are made available as open-source software.Computer Systems, Imagery and Medi
Interactive graph drawing with constraints
This thesis investigates the requirements for graph drawing stemming
from practical applications, and presents both theoretical as
well as practical results and approaches to handle them.
Many approaches to compute graph layouts in various drawing styles
exist, but the results are often not sufficient
for use in practice. Drawing conventions, graphical notation standards,
and user-defined requirements restrict the set of admissible
drawings. These restrictions can be formalized as constraints for the
layout computation. We investigate the requirements and give an overview
and categorization of the corresponding constraints.
Of main importance for the readability of a graph drawing is
the number of edge crossings. In case the graph is planar
it should be drawn without crossings, otherwise we should
aim to use the minimum number of crossings possible.
However, several types of constraints may impose
restrictions on the way the graph can be embedded in the plane.
These restrictions may have a strong impact on crossing minimization.
For two types of such constraints we present specific solutions
how to consider them in layout computation:
We introduce the class of so-called embedding constraints, which
restrict the order of the edges around a vertex.
For embedding constraints we describe approaches for planarity testing,
embedding, and edge insertion with the minimum number of crossings. These problems
can be solved in linear time with our approaches.
The second constraint type that we tackle are clusters. Clusters
describe a hierarchical grouping of the graph's vertices that
has to be reflected in the drawing. The complexity of the
corresponding clustered planarity testing problem for
clustered graphs is unknown so far.
We describe a technique to compute a maximum clustered planar
subgraph of a clustered graph. Our solution
is based on an Integer Linear Program (ILP) formulation and includes
also the first practical clustered planarity test for general clustered
graphs. The resulting subgraph can be used within the first step of
the planarization approach for clustered graphs.
In addition, we describe how to improve the performance
for pure clustered planarity testing by implying a branch-and-price
approach.
Large and complex graphs nowadays arise in many application domains.
These graphs require interaction
and navigation techniques to allow exploration of the underlying data.
The corresponding concepts are presented and solutions for three
practical applications are proposed: First, we describe Scaffold Hunter,
a tool for the exploration of chemical space. We show how to use
a hierarchical classification of molecules for the visual navigation in chemical space.
The resulting visualization is embedded into an interactive environment
that allows visual analysis of chemical compound databases.
Finally, two interactive
visualization approaches for two types of biological networks, protein-domain
networks and residue interaction networks, are presented.In zahlreichen Anwendungsgebieten werden Informationen als Graphen modelliert und
mithilfe dieser Graphen visualisiert. Eine ĂŒbersichtliche Darstellung hilft
bei der Analyse und unterstĂŒtzt das VerstĂ€ndnis
bei der PrÀsentation von Informationen mittels graph-basierter Diagramme.
Neben allgemeinen Ă€sthetischen Kriterien bestehen fĂŒr eine solche Darstellung
Anforderungen, die sich aus der Charakteristik der Daten, etablierten Darstellungskonventionen
und der konkreten Fragestellung ergeben. ZusÀtzlich ist hÀufig eine
individuelle Anpassung der Darstellung durch den Anwender gewĂŒnscht. Diese Anforderungen können mithilfe von Nebenbedingungen
fĂŒr die Berechnung eines Layouts formuliert werden.
Trotz einer Vielzahl unterschiedlicher Anforderungen aus zahlreichen Anwendungsgebieten können die meisten Anforderungen ĂŒber einige generische Nebenbedingungen formuliert werden.
In dieser Arbeit untersuchen wir die Anforderungen
aus der Praxis und beschreiben eine Zuordnung zu Nebenbedingungen fĂŒr
die Layoutberechnung. Wir geben eine Ăbersicht ĂŒber den aktuellen
Stand der Behandlung von Nebenbedingungen beim Zeichnen von Graphen
und kategorisieren diese nach grundlegenden Eigenschaften.
Von besonderer Wichtigkeit fĂŒr die QualitĂ€t einer Darstellung ist die
Anzahl der Kreuzungen. Planare Graphen sollten kreuzungsfrei gezeichnet
werden, bei nicht-planaren Graphen sollte die minimale Anzahl Kreuzungen
erreicht werden. Einige Nebenbedingungen beschrÀnken jedoch die
Möglichkeit, den Graph in die Ebene einzubetten. Dies kann starke
Auswirkungen auf das Ergebnis der Kreuzungsminimierung haben.
Zwei wichtige Typen solcher Nebenbedingungen werden in dieser Arbeit nÀher
untersucht. Mit den Embedding Constraints fĂŒhren wir eine Klasse
von Nebenbedingungen ein, welche die mögliche Reihenfolge der Kanten um einen Knoten
beschrĂ€nken. FĂŒr diese Klasse prĂ€sentieren wir Linearzeitalgorithmen
fĂŒr das Testen der PlanaritĂ€t und das optimale EinfĂŒgen von Kanten
unter Beachtung der EinbettungsbeschrÀnkungen.
Der zweite Typ von Nebenbedingungen sind Cluster, die eine hierarchische
Gruppierung von Knoten vorgeben. FĂŒr das Testen der Cluster-PlanaritĂ€t unter
solchen Nebenbedingungen ist die KomplexitÀt bisher unbekannt.
Wir beschreiben ein Verfahren, um einen maximalen Cluster-planaren
Untergraphen zu berechnen.
Wir nutzen dabei eine Formulierung als ganzzahliges lineares Programm
sowie einen Branch-and-Cut Ansatz zur Lösung. Das Verfahren erlaubt
auch die Bestimmung der Cluster-PlanaritÀt und
stellt damit den ersten praktischen Ansatz zum Testen
allgemeiner Clustergraphen dar. ZusÀtzlich
beschreiben wir eine Verbesserung fĂŒr den Fall, dass lediglich Cluster-PlanaritĂ€t
getestet werden muss, der maximale Cluster-planare Untergraph aber nicht
von Interesse ist. FĂŒr dieses Szenario geben wir eine vereinfachte Formulierung
und prÀsentieren ein Lösungsverfahren, das auf einem Branch-and-Price Ansatz beruht.
In der Praxis mĂŒssen hĂ€ufig sehr groĂe oder komplexe Graphen untersucht
werden. Dazu werden entsprechende Interaktions- und Navigationsmethoden
benötigt. Wir beschreiben die entsprechenden Konzepte und stellen Lösungen
fĂŒr drei Anwendungsbereiche vor:
ZunÀchst beschreiben wir Scaffold Hunter, eine Software zur Navigation
im chemischen Strukturraum. Scaffold Hunter benutzt eine hierarchische
Klassifikation von MolekĂŒlen als Grundlage fĂŒr die visuelle Navigation.
Die Visualisierung ist eingebettet in eine interaktive OberflÀche die
eine visuelle Analyse von chemischen Strukturdatenbanken erlaubt.
FĂŒr zwei Typen von biologischen Netzwerken, Protein-DomĂ€nen Netzwerke
und Residue-Interaktionsnetzwerke, stellen wir AnsĂ€tze fĂŒr die interaktive
Visualisierung dar. Die entsprechenden Layoutverfahren unterliegen einer
Reihe von Nebenbedingungen fĂŒr eine sinnvolle Darstellung