Roland Häggkvist founded the research group in Discrete Mathematics, and has been very influential in the development of the mathematics department. He will be remembered by colleagues as an outspoken, genereous, and brilliant mathematician
Roland Häggkvist
ImagePer-Håkan LundowRoland Häggkvist was appointed as professor in Discrete Mathematics at Umeå University in 1989 and remained in that position until his retirement in 2017. He studied under Gabriel Andrew Dirac in Aarhus, Denmark while under the nominal supervision of Hans Wallin at Umeå university. He defended his PhD thesis entitled On Factors and Cycles in Graphs and Digraphs at the department of mathematics in Umeå in 1977.
After working at Cambridge, Rutgers and Waterloo, he later returned to Sweden and held positions at KTH and Stockholm University before he came back to Umeå in 1989 as one of a group of new professors funded by a government program to support the development of information technology.
An innovative aspect of Roland’s research was his early use of computational methods in graph theory, a novel approach at the time. Roland’s influence in this respect can still be seen in some of the work of his former students, and in particular in research involving large-scale computations that has been carried out using the resources of High Performance Computing Center North (HPC2N) in Umeå.
Roland supervised two PhD students in Stockholm and twelve in Umeå across a range of topics within discrete mathematics, from graph theory and design theory, to the interaction between discrete mathematics and statistical physics.
Roland collaborated with a wide range of people and had frequent research visitors in Umeå. The research group that he built in Umeå has since had connections and research collaborations with mathematicians from many parts of the world. Among the most frequent collaborators are Pavol Hell, Herbert Fleischner, Amanda Chetwynd, Andrew Thomason, Bela Bollobas, and David Daykin.
Besides his many papers on Graph theory and Combinatorics, Roland also made well-cited contributions to Statistical methods and Algebra. The most well known contribution by Roland that carries his name is the so called Caccetta-Häggkvist conjecture [1] together with Louis Caccetta, stating that every simple digraph of order n with minimum outdegree at least r has a cycle of length at most the ceiling of n/r. Roland also wrote a well received and influential book on bipartite graphs and their applications together with Armen Asratian and Tristan Denley [2].
[1] L. Caccetta and R. Häggkvist. On minimal digraphs with given girth. Congressus Numerantium, XXI, 1978.
[2] A. Asratian, T. M. J. Denley, R. Häggkvist, Bipartite graphs and their applications, Cambridge University Press, 1998.