Miloslav Znojil
The method of Hill determinants in PT-symmetric quantum mechanics
in
``Recent Trends in Exponential Asymptotics" ,
ed. Y. Takei,
RIMS Kokyuroku series
vol. 1424 (2005) pp. 240 - 253
(math-ph/0410009, proceedings of the conference held in RIMS, Kyoto, June 28 - July 2, 2004)