On Upward Drawings of Trees on a Given Grid

Computing a minimum-area planar straight-line drawing of a graph is known to be NP-hard for planar graphs, even when restricted to outerplanar graphs. However, the complexity question is open for trees. Only a few hardness results are known for straight-line drawings of trees under various restrictions such as edge length or slope constraints. On the other hand, there exist polynomial-time algorithms for computing minimum-width (resp., minimum-height) upward drawings of trees, where the height (resp., width) is unbounded. In this paper we take a major step in understanding the complexity of the area minimization problem for strictly-upward drawings of trees, which is one of the most common styles for drawing rooted trees. We prove that given a rooted tree $T$ and a $W\times H$ grid, it is NP-hard to decide whether $T$ admits a strictly-upward (unordered) drawing in the given grid.Comment: Appears in the Proceedings of the 25th International Symposium on Graph Drawing and Network Visualization (GD 2017

Interactive visualization of information hierarchies and applications on the web

The visualization of information hierarchies is concerned with the presentation of abstract hierarchical information about relationships between various entities. It has many applications in diverse domains such as software engineering, information systems, biology, and chemistry. Information hierarchies are typically modeled by an abstract tree, where vertices are entities and edges represent relationships between entities. The aim of visualizing tree drawings is to automatically produce drawings of trees which clearly reflect the relationships of the information hierarchy. This thesis is primarily concerned with problems related to the automatic generation of area-efficient grid drawings of trees, interactively visualizing information hierarchies, and applying our techniques on Web data. The main achievements of this thesis include: 1. An experimental study on algorithms that produce planar straight-line grid drawings of binary trees, 2. An experimental study that shows the algorithm for producing planar straight-line grid drawings of degree-d trees with n nodes with optimal linear area and with user-defined arbitrary aspect ratio, works well in practice, 3. A rings-based technique for interactively visualizing information hierarchies, in real-time, 4. A survey of Web visualization systems developed to address the lost in cyberspace problem, 5. A separation-based Web visualization system that we present as a viable solution to the lost in cyberspace problem, 6. A rings-based Web visualization system that we propose as a solution to the lost in cyberspace problem

How to fit a tree in a box

We study compact straight-line embeddings of trees. We show that perfect binary trees can be embedded optimally: a tree with n nodes can be drawn on a vn by vn grid. We also show that testing whether a given rooted binary tree has an upward embedding with a given combinatorial embedding in a given grid is NP-hard.Peer ReviewedPostprint (author's final draft

Tree Drawings Revisited

We make progress on a number of open problems concerning the area requirement for drawing trees on a grid. We prove that 1) every tree of size n (with arbitrarily large degree) has a straight-line drawing with area n2^{O(sqrt{log log n log log log n})}, improving the longstanding O(n log n) bound; 2) every tree of size n (with arbitrarily large degree) has a straight-line upward drawing with area n sqrt{log n}(log log n)^{O(1)}, improving the longstanding O(n log n) bound; 3) every binary tree of size n has a straight-line orthogonal drawing with area n2^{O(log^*n)}, improving the previous O(n log log n) bound by Shin, Kim, and Chwa (1996) and Chan, Goodrich, Kosaraju, and Tamassia (1996); 4) every binary tree of size n has a straight-line order-preserving drawing with area n2^{O(log^*n)}, improving the previous O(n log log n) bound by Garg and Rusu (2003); 5) every binary tree of size n has a straight-line orthogonal order-preserving drawing with area n2^{O(sqrt{log n})}, improving the O(n^{3/2}) previous bound by Frati (2007)

Enumeration of Independent Sets in Graphs

An independent set is one of the most natural structures in a graph to focus on, from both a pure and applied perspective. In the realm of graph theory, and any concept it can represent, an independent set is the mathematical way of capturing a set of objects, none of which are related to each other. As graph theory grows, many questions about independent sets are being asked and answered, many of which are concerned with the enumeration of independent sets in graphs. We provide a detailed introduction to general graph theory for those who are not familiar with the subject, and then develop the basic language and notation of independent set theory before cataloging some of the history and major results of the field. We focus particularly on the enumeration of independent sets in various classes of graphs, with the heaviest focus on those defined by maximum and minimum degree restrictions. We provide a brief, specific history of this topic, and present some original results in this area. We then speak about some questions which remain open, and end the work with a conjecture for which we provide strong, original evidence. In the appendices, we cover all other necessary prerequisites for those without a mathematical background

Quad general tree drawing algorithm and general trees characterization: towards an environment for the experimental study on general tree drawing algorithms

Information visualization produces (interactive) visual representations of abstract data to reinforce human cognition and perception; thus enabling the viewer to gain knowledge about the internal structure of the data and causal relationships in it. The visualization of information hierarchies is concerned with the presentation of abstract hierarchical information about relationships between various entities. It has many applications in diverse domains such as software engineering, information systems, biology, and chemistry. Information hierarchies are typically modeled by an abstract tree, where vertices are entities and edges represent relationships between entities. The aim of visualizing tree drawings is to automatically produce drawings of trees which clearly reflect the relationships of the information hierarchy. This thesis is primarily concerned with introducing the new general tree drawing algorithm Quad that produces good visually distinguishable angles, and a characterization of general trees which allows us to classify general trees into several types based on their characteristics. Both of these topics are part of building an experimental study environment for the evaluation of drawing algorithms for general trees. The main achievements of this thesis include: 1. A study on characterization of general trees that aims to classify them into several types. 2. A tree drawing algorithm that produces visually distinguishable angles for high degree general trees with user specified angular coefficient

Finding Fibonacci : an interdisciplinary liberal arts course based on mathematical patterns

The purpose of this study was to design, teach, and evaluate an undergraduate interdisciplinary mathematics course based on certain patterns, primarily the Fibonacci sequence. Rationale for the course includes the benefits of connected learning and the scarcity of liberal arts courses based on mathematics. The course is intended to emphasize pattern exploration in mathematics as well as in other disciplines. It is hoped that students in the course will find connections between mathematics and history, art, architecture, music, literature, nature, and economics. Course design includes a syllabus, student textbook, and sample lesson plans. The student textbook explores mathematical connections with the Fibonacci sequence such as the golden ratio, Pascal\u27s triangle, Pythagorean triples, combinatorics, and fractal geometry. Historical background of Leonardo Fibonacci\u27s life and times in the High Middle Ages is used to introduce the course. Applications of Fibonacci numbers in art, architecture, music, literature, nature, and economics are discussed. Students are asked to assess the meaning of these connections in light of their liberal arts experience. Evaluation of the course, primarily qualitative in nature, gives evidence that the pilot offering of the course enabled students to see relationships between various fields of study in a new way