Some explanation for coupling_steering.pdf

Differences between serial and parallel coupling in a nutshell.
F and S refer to the first and the second participant, respectively.  
Code parts that belong to the solver itself are marked in red. 
Data exchange is marked in blue.  
WID stands for WriteInitialData.

More information in Benjamin's thesis, Section 3.5
https://mediatum.ub.tum.de/doc/1320661/document.pdf
