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International Credit Mobility grant brings mathematicians together in Leiden

Leiden and South Africa have long standing historical ties in the field of mathematics. These ties have now been strengthened thanks to an Erasmus+ International Credit Mobility (ICM) grant. Four researchers from Pretoria are now visiting Leiden. ‘No matter how good we are at dealing with Teams and Zoom, you can’t replace face-to-face contact,’ says mathematician Marcel de Jeu.

De Jeu specialises in Positivity, a field of mathematics that focuses on ordered structures and their applications. ‘These kinds of order occur very naturally in all sorts of models in mathematics and economics. Many models have a natural order, for example the density of a bacteria population. This is always positive: if a model predicts a negative density, something is wrong.’

Sacred ground

Positivity is strongly represented in both Leiden and South Africa. ‘Leiden is a kind of sacred ground for Positivity,’ says De Jeu. ‘Adriaan Zaanen was professor here from 1956 to 1981. He was one of the founders of the field.’ In the 1950s it was customary for Afrikaans-speaking South Africans to come to the Netherlands to do their PhD. This is how Zaanen ended up with a number of PhD candidates from South Africa. These later moved back to their homeland, which explains the amount of knowledge about Positivity in South Africa, in Pretoria in particular.

Real-life visit

The ICM grant has helped further strengthen the ties and develop collaboration projects. Four researchers from Pretoria are now visiting Leiden, for example. Professor Jan Harm van der Walt is one of them. ‘Through an exchange with another university, you broaden your perspective and learn about another culture.’

Jan Harm van der Walt and Marcel de Jeu.

Van der Walt and De Jeu have a joint PhD candidate in Pretoria, who is now also in Leiden. ‘Now the three of us really can work together,’ says De Jeu. ‘Standing at the board together, popping in if you want to discuss something: a real-life visit like this is irreplaceable.’


An unintended effect of the grant has been to bring other researchers to Leiden. ‘We suddenly have such a mass that it is interesting for other researchers to meet up here,’ De Jeu explains. ‘Someone from Dresden has already visited, and another four researchers will be visiting in the next few months.’

International Credit Mobility grant

The European Erasmus+ International Credit Mobility is a programme that enables exchanges between bachelor’s and master’s students, PhD candidates and staff from universities outside the European Union. If you are interested, why not apply for the Erasmus+ International Credit Mobility (ICM) grant? Let grant adviser Kathelijne Smits know that you are interested before 2 December by sending an Expression of Interest. See here for more information.

Text: Dagmar Aarts
Banner photo: Jacaranda, a famous tree from Pretoria. Foto: Tim Cooper on Unsplash

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