TY  - RPRT
TI  - Studies in perturbation theory. ix - connection between various approaches in the recent development - evaluation of upper bounds to energy eigenvalues in schroedinger's perturbation theory.
AU  - Loewdin, P.-O.
PY  - 1965
UR  - https://ntrs.nasa.gov/citations/19650050736
ID  - 19650050736
ER  -