The talk **Rational harmonic functions and their applications in gravitational lensing**, by Prof. Dr. Jörg Liesen, will be held on Thursday September 24, 2015 at 09:00 in lecture room K3, 2. floor.

This special MORE seminar is organized jointly with Computational Mathematics Seminar (Institute of Computer of Science), also as special seminar on continuum mechanics, as an activity of the Necas Center for mathematical modeling.

**Abstract**

This talk will discuss recent results on the zeros of rational harmonic functions f(z)=r(z)-conj{z}, which have fascinating applications ranging from numerical linear algebra to astrophysics. A particular focus will be on extremal functions, where r(z) is of degree n>=2 and f(z) has the maximal possible number of 5n-5 zeros. Examples of such functions will be visualized using phase portraits, and the implication of our theoretical results in the theory of graviational lensing will be discussed.