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Leipzig University

Dr. Martin Ritzert

I am a Junior Group Leader at ScaDS.AI at Leipzig University. My research revolves around machine learning of graph data where I am interested in how to generate graphs (especially combined with other modalities such as 3D information and fine details), how to apply graph learning methods to traditional relational databases, and how to train message-passing networks (the main paradigm for graph learning) to approximate traditional algorithms for combinatorial problems such as the 3-coloring problem.

I am currently looking for people to write their BSc or MSc thesis on problems related to graph machine learning. Please reach out to me via email.

There is an open PhD position in my group, see: PhD in Graph Machine Learning.

Research Interests

I am generally interested in machine learning and in particular machine learning on graph data. Graphs are a very general data structure and can be used to model many different types of data, such as social networks, molecules, and 3D scans of neurons or botanical trees. Some concrete topics are:

  • Graph Generation
  • Machine learning on relational databases
  • Learned approximation (message-passing) algorithms for NP-hard problems (e.g. 3-coloring)
  • Benchmarks for graph machine learning

I am further interested in complexity, learning theory, graph theory, and lately clustering, especially hierarchical clustering.

Possible thesis projects:

  • Similarity Measures for botanical trees capturing 3D information and structure
  • Graph Transformers for neurons and botanical trees
  • Graph Drawing using Graph Machine Learning
  • GNNs with registers (generalizing virtual nodes)
  • Your own idea

Projects

There are two main projects running at the moment.

Generating Trees

The project on generating trees aims to create a generative model for dendritic trees of neurons and botanical trees. In contrast to many works to generate such shapes, we aim to use graph-learning methods that focus on the structure (i.e. branching pattern) of the tree first and the positions second. A core challenge for these kinds of datasets is that branches may be positioned close to each other without being connected – in contrast for molecules, which are currently the main application of graph generation, atoms that are close by do share a bond (or rather: the distance between two atoms in a molecule defines whether they are connected by a chemical bond, the direction does not matter here). In contrast to generating e.g. an office scene, trees and neurons contain much finer detail and are way more sparse. The main methods used in the project are based on graph diffusion.

Machine Learning on Relational Databases

One (surprisingly common) way to apply machine learning to databases is to essentially join all tables into a very big one which can then be send to an LLM. While this approach works to a degree and for some kind of databases, it completely ignores the structure of the database and creates a lot of redundant data (e.g. the address and capacity of the Leipzig Stadium will be repeated for all home matches of RB Leipzig). By working directly on the hypergraph defined by the database, one can train machine learning models that can extract information directly from the database. We are currently investigating how to best create the hypergraph in a way that it is useful for machine learning while also not becoming too large so it will still work on large databases.

Curriculum Vitae

  • since 2026: Junior Group Leader at ScaDS.AI
  • 2022-2025: Postdoc at Georg-August University Göttingen
  • 2021-2022: Postdoc at Aarhus University, Denmark
  • 2016-2021: PhD at RWTH Aachen University
  • 2011-2016: BSc and MSc Computer Science at RWTH Aachen University
funded by:
Gefördert vom Bundesministerium für Bildung und Forschung.
Gefördert vom Freistaat Sachsen.