Implement an exact Weidenmüller formula
D. Dresen and F. Hassler have derived an exact version of Weidenmüller formalism, see this master thesis.
Applied to a single energy it is exactly the same as what we do currently in Kwant (up to issues of efficient order of Gaussian elimination), however having this formalism implemented may allow for more efficient approximate calculations in tunneling regime
Edited by Anton Akhmerov