Quantum Mechanics in one-dimensional space enables us to
understand resonances via ordinary differential Schroedinger
equation containing a suitable model potential V(r). Authors
choose a specific two-parametric piecewise-constant double-barrier
V(r) supporting two unbound states with equal energies and
half-lives. Numerically they construct the complex energy surfaces
in the vicinity of the exceptional point of degeneracy.  A change
of variables enables them to clarify the changes of identity of
the poles of the S-matrix. The crossing and anticrossing of the
two energies and of their widths becomes clearly visualized in
this manner.

MR2252702 Hernández, E.; Jáuregui, A.; Mondragón, A. Non-Hermitian
degeneracy of two unbounded states. J. Phys. A 39 (2006), no. 32,
10087--10105. 81U05