Stephan Schwartz successfully defended his dissertation “Optimal Graph Coverings with Connected Subgraphs” at the Institute of Mathematics at Freie Universität Berlin on March 29, 2023. The thesis is a result of Stephan’s work in a series of projects on optimal toll enforcement for the Federal Logistics and Mobility Office (BALM). In particular, Stephan worked on the optimal design of control segments for BALM’s mobile toll enforcement units; their form has a huge impact on the efficiency of staff scheduling. The underlying mathematical problem belongs to the family of graph covering (or partitioning) problems. The dissertation makes fundamental contributions to their efficient solution, in particular, to the approximation of balanced node coverings and the treatment of connectivity requirements. Stephan will continue to work on optimal enforcement at ZIB spin-off LBW Optimization GmbH. 

The photo shows (from left to right) Karin Schaller (committee member), Timo Berthold (external committee member from TU Berlin), Stephan Schwartz, Ralf Borndörfer (promoter and committee head), and Heike Siebert (committee member).  

Link to toll enforcement project: https://www.zib.de/projects/optimization-toll-control-tours