Obituary for Anders Thorup

Anders was for more than half a century a very active and central employee, first at the former Department of Mathematics, which later developed into the current Department of Mathematical Sciences.

Anders graduated from Christianshavns Gymnasium in 1961 and began studying mathematics at the University of Copenhagen the same year. He graduated with an MSc in 1966 and a mag.scient. in 1968. In addition to working as an instructor, he was appointed amanuensis in 1968 and then associate professor in 1969 until his retirement in 2013.

Anders wrote his master's thesis in classical algebra under the supervision of Chr. U. Jensen, but since then algebraic geometry became his main research interest. A study programme at the University of Warwick gave him many international academic contacts, and he worked with leading foreign researchers, including Steve Kleiman (MIT) and Dan Laksov (KTH Royal Institute of Technology). Together with Kleiman, a generalised Buchsbaum-Rim multiplicity theory based on algebraic geometry was developed. Together with Laksov, Anders organised a year at the Institut Mittag-Leffler and they published 13 papers on various topics, mainly in algebraic geometry.

In addition to a strong interest in understanding mathematical problems via as general an approach as possible, Anders also had a lifelong taste and penchant for concrete problems. For example, we could mention very early work with Børge Jessen on translational equivalence between polyhedra, just as Ian Kiming from later years remembers a discussion about solutions to the Diophantine equation y^2 + 1 = 2x^3 that Anders encountered in connection with another problem.

In recent years, Anders returned to classical ring and module theory, where he worked with Chr. U. Jensen and Søren Jøndrup on a couple of papers.

In addition to being an excellent researcher, Anders was an excellent teacher and author of lecture notes. Both as a lecturer and author, his presentation was clear and precise down to the smallest detail. He wrote widely used lecture notes for 1st year analysis, algebra (Mat 2AL), algebraic geometry and number theory. The notes in commutative algebra were of great benefit to Søren Jøndrup as a lecturer.

As a student, I (Ian Kiming) had Anders as my algebra teacher and remember Anders' lectures for their clarity and preparedness. The lecture notes and many of the problem-solving sessions were also peppered with inspiring ideas that pointed out of the syllabus and towards more advanced topics. A lasting influence for me and a model I have adopted was seeing Anders' standard for lectures, which, in addition to clarity, consisted of having prepared the lecture so thoroughly that you can deliver it without the use of notes.

Both as a teacher and colleague, the lasting impression Anders made can be summarised with the words openness, availability and helpfulness. If a student came to him with a problem they wanted to discuss, the door was always open and he took the time, whether the question was about a course topic or something completely different. This helpfulness also extended to colleagues: many employees have benefited from his help with computer problems, and they never went in vain. Anders was an active emeritus who, among other things, undertook the task of maintaining the department's digital archive of course notes, PhD theses etc.

During Chr. U. Jensen's long period of illness, Anders proved to be a role model when it comes to taking responsibility when loved ones are in need of help. Anders made an enormous effort and was also the decisive driving force in organising a group of visitors for Chr. U., of which both of us were a part. We were both impressed by the amount of energy Anders put into making sure Christian was doing well.

Until a few years ago, Anders, Christian U. and Søren Jøndrup met every Wednesday at the department, where they took turns presenting what they had done in maths the previous week. However, there was also time to discuss many other problems.

Anders had a great love of nature and together with SJ enjoyed spending time together in their holiday homes by Sejerøbugten.

Anders is greatly missed both as a colleague and as a person.

Søren Jøndrup and Ian Kiming