Johannes RauWorking group GeometryDepartment of Mathematics 
I work at the mathematics department at the University of Tübingen, Germany. In summer term 2019, I fill a deputy professorship in mathematical physics. My research area is tropical geometry and its connections to enumerative geometry, real algebraic geometry and intersection theory. More general, my mathematical interests focus on algebraic geometry, symplectic geometry and combinatorics. For more details, please check out the other sections and contact me.
Email: johannes.rau (at) math.unituebingen.de
Construct your own real algebraic curve using this simple browser app ;)
I write a book on tropical geometry together with Grigory Mikhalkin. You can find a draft version here. Comments and corrections are highly welcome.
My research area is tropical geometry (the fancy adjective tropical was originally used in the context of the maxplus algebra to honour earlier work of the Brazilian (Hungarianborn) mathematician Imre Simon). Even though the origins of the field are much older, tropical geometry emerged as an new development in algebraic and symplectic geometry around 2000. Here is a list of keywords describing my research interests.
Tropical mathematics can be compared to the world of dinosaurs. When paleontologists want to learn more about these animals, they can't just watch them them in the zoo or the jungle, because unfortunately the poor things became extinct a long time ago. Instead, they work more like archeologists. They go digging for their bones, try to reassemble their skeletons, and from that draw conclusions about how these animals looked like, what they ate, how they hunted etc. In tropical geometry, we do exactly the same!
In our setting, the dinosaurs are called algebraic varieties. These are complicated geometrical shapes given by polynomial equations. Such algebraic varieties show up all the time in mathematics, science and real life, and therefore their study forms one of the oldest and most sophisticated fields in mathematics (called algebraic geometry). Algebraic varieties are often so complicated that it is impossible to get our hands on them directly – like the extinct dinosaurs. However, in some cases mathematicians found a way to get hands on the skeletons of these mathematical dinosaurs. Technically, you first have to turn the dinosaurs into amoebas and then starve them out until only the skeletons are left – this is where the analogy gets a little violent ;).
The mathematical skeletons are called tropical varieties, and in tropical geometry we play paleontologist and try to find out more about the original geometrical objects by studying their tropical skeletons (you can find some pictures on this page). The nice thing is that tropical varieties are much simpler objects than the original ones and can be studied in much more downtoearh terms. Of course, we cannot work wonders and find answer all questions (it is easy to estimate the size of the reallife dinosaur from its skeleton, but did it have furry or smooth skin?), but by now some remarkable facts about algebraic varieties were deduced from the study of their tropical skeletons, and that is why tropical geometry is nowadays such an exciting and rapidly growing field.
You are bachelor/master student in mathematics (or a researcher from a different field) and want to embark on a first expedition to the tropics? Then have a look at these lecture notes.
These notes grew out of a lecture series I gave for bachelor students without any prior knowlwedge of the topic. They are therefore on a very elementary level and give priority to intution and illustrations as opposed to rigour and depth.One of the origins of tropical geometry is Viro's patchworking method. The link below leads to a small browser app which allows you to do some experiments with this method.
You can use it to create your own real algebraic curves and pictures like the one to the right.
Courses
(Pro)Seminars
Working group seminars

johannes.rau (at) math.unituebingen.de Postal address
Johannes Rau 
Phone
Phone: +49 (0)7071 29 78572 Office
Room C5 P43 