GD2026 PhD School
Lecturers
Prof. Dr. Reyan Ahmed
University of Arizona, United States
Title: Graph sparsification and its application to network visualization
Abstract:
we explore recent advancements in large network visualization through the lens of graph spanners and related techniques. The first topic introduces a generalized multi-level sparsification approach that enhances connectivity among vertices with varying importance, extending traditional methods such as spanning trees and Steiner trees. The second topic focuses on the construction of spanners in weighted graphs, addressing the challenges of preserving distances with additive errors while demonstrating how classic spanner constructions can be effectively adapted for improved efficiency. Next, we present a novel algorithm for creating scalable, readable tree layouts, emphasizing the minimization of edge crossings and label overlaps while optimizing edge lengths and compactness. Collectively, these topics provide valuable insights into leveraging graph spanners for the effective visualization of complex relational datasets and enhancing our understanding of large networks. Finally, we present an approach that optimizes multiple readability criteria simultaneously in network visualizations. Unlike traditional visualization methods that focus on a single criterion, this approach flexibly supports both smooth and non-smooth optimization objectives, including stress, edge lengths, neighborhood preservation, and angular resolution. Experimental results demonstrate that the approach improves graph readability and produces high-quality layouts across diverse visualization tasks.
Biography:
Reyan Ahmed is an assistant professor at the computer science department of the University of Arizona. He received his Ph.D. from the same department in 2021. Before that he has received his M.Sc. and B.Sc. from the department of computer science and engineering of Bangladesh University of Engineering and Technology. His research interests include graph algorithms, network visualization, and data science.
Prof. Dr. Will Evans
University of British Columbia, Canada
Title: TBA
Abstract:
Suppose we create a partial order on the vertices and edges of an undirected graph G by saying that vertex v is less than edge e if and only if v is an endpoint of e in G. This is only a partial order since we can't tell, for example, which of two different vertices is less than the other. The dimension of such a partial order is the minimum number of total orders on vertices and edges whose intersection is the partial order. In 1989 Walter Schnyder published a paper showing that G is a planar graph if and only if the dimension of its partial order is at most three. We'll talk about how this leads to an elegant method (also due to Schnyder) for drawing planar graphs using small integer coordinates and how it can be used to create representations of graphs as the contact of simple objects.Biography:
Dr. William (Will) Evans is a Professor Emeritus of Computer Science at the University of British Columbia (UBC). He obtained his B.Sc. in computer science (1987) from Yale University and his Ph.D. in computer science (1994) from University of California, Berkeley under the supervision of Dr. Manuel Blum. He was a postdoc at UBC for two years with Dr. Nick Pippenger then an Assistant Professor at the University of Arizona for four years. He returned to UBC in 2001 and became a Full Professor Emeritus in 2025.
Prof. Dr. Md. Saidur Rahman
Bangladesh University of Engineering and Technology (BUET), Bangladesh
Title: Drawing Planar Graphs
Abstract:
A graph is planar if it can be drawn or embedded in the plane so that no two edges intersect geometrically except at a vertex to which they are both incident. A plane graph is a planar graph with a fixed planar embedding in the plane. A drawing problem X for a plane graph G asks to determine whether G has a drawing D satisfying a set P of given properties and to find D if it exists. The corresponding problem for a planar graph G asks to determine whether G has a planar embedding that has a drawing D satisfying the set P of properties and find D if it exists. If every embedding of G has a drawing D satisfying P, then the problem is trivial, i.e., the problem for plane graphs and that for planar graphs are the same. Otherwise, the problem for planar graphs becomes difficult even if an efficient solution of the problem for a plane graph exists since a planar graph may have an exponential number of planar embeddings. Various techniques are found in literature that are used to solve the drawing problems for planar graphs. In this talk, we discuss three of the widely used techniques, namely, (i) reduction to planarity testing, (ii) incremental modification and (iii) SPQR-tree decomposition.
Biography:
Md. Saidur Rahman, a professor (on deputation) of Bangladesh University of Engineering and Technology (BUET) and a fellow of Bangladesh Academy of Sciences, is currently serving as a member of University Grants Commission of Bangladesh. He is a renowned researcher in the field of graph algorithms and is regarded as an authority on graph drawing algorithms. He has more than 140 publications on algorithms and graph theory in internationally reputed journals and conferences. He has developed many efficient algorithms for finding rectangular drawings, box-rectangular drawings, orthogonal drawings, monotone drawings, minimum-segment drawings, minimum-area drawings for planar graphs which have enormous applications in VLSI layout automation, software engineering, DNA recognition, etc. His graduate textbook “Planar Graph Drawing,” written with renowned computer scientist Professor Takao Nishizeki, is considered as the most valuable pioneering work in planar graph drawings. He has co-edited five volumes of LNCS series of Springer and served as guest editors for several reputed journals. His undergraduate textbook “Basic Graph Theory” which has been published by Springer has become very popular among students and researchers. Professor Rahman is leading an enthusiastic research group in Graph Drawing and Information Visualization Laboratory of CSE Department, BUET. He has supervised four Ph. D. theses and 24 M. Sc. Engg. theses. He is a recipient of “BAS Gold Medal 2003” in the junior group, “UGC Award 2004” and the prestigious “Funai Information Technology Award for Young Researchers 2004.” He is a distinguished member of ACM.
Prof. Dr. Alessandra Tappini
University of Perugia, Italy
Title: Hybrid Graph Visualizations: From Theory to Practice and Back
Abstract:
Hybrid graph visualizations combine the classical node-link paradigm with alternative drawing styles within a single layout. Node-link diagrams are used to show the global structure of a network, while dense portions are represented using other paradigms, such as adjacency matrices or chord diagrams, to mitigate the visual clutter caused by edge crossings. This lecture will present a research perspective on hybrid graph visualization as a graph drawing topic at the intersection of theory and practice. It will discuss how practical visualization challenges motivate new theoretical questions, and how algorithmic and combinatorial foundations can guide the design of effective visualization techniques. Through selected examples from the literature, we will examine key models, algorithmic problems, and experimental user evaluations for hybrid visualizations, highlighting both established results and open challenges.
Biography:
Alessandra Tappini is an Assistant Professor in the Department of Engineering at the University of Perugia. Her research focuses on graph drawing from both theoretical and applied perspectives, with additional interests in algorithmic graph theory and information visualization. She earned her PhD in Industrial and Information Engineering from the University of Perugia in 2020 under the supervision of Giuseppe Liotta. From 2020 to 2025, she served as a postdoctoral researcher at the same institution.
Prof. Dr. Carola Wenk
Tulane University, United States
Title: Geometric Graph Similarity: Distances, Matchings, and Algorithms
Abstract:
Geometric graphs arise naturally in applications such as road and river networks, transportation systems, biological structures, trajectories, plant morphology, and commodity networks. Comparing such graphs requires distance measures that capture both geometry and topology while remaining robust to noise, different levels of detail, and non-isomorphic graph structure. This lecture will survey distance measures for embedded and immersed graphs, including planar embedded graphs and graphs with well-behaved crossings. We will discuss algorithmic approaches and hardness results, with a particular focus on the mappings or matchings induced between the graphs, rather than only on the resulting distance value. We will also highlight approaches from topological data analysis that define signatures and distances for comparing geometric graphs. The lecture will conclude with open problems and challenges in developing distances that are mathematically well-founded, computationally tractable, and useful in applications.
Biography:
Carola Wenk is a Professor of Computer Science at Tulane University. Her research is in computational geometry, with a focus on algorithms for shape matching, curves, trajectories, and geometric graphs. She is particularly known for her work on the Fréchet distance and related similarity measures, including applications to map matching, trajectory analysis, and comparison of embedded geometric structures. Her work combines algorithmic foundations with applications in geospatial data analysis, movement modeling, and biomedical imaging.