TY  - RPRT
TI  - A variational principle for the scattered wave.
AU  - D E Freund
AU  - R A Farrell
PY  - 1990
DO  - 10.1121/1.399311
UR  - https://pubmed.ncbi.nlm.nih.gov/2348017/
ID  - 2348017
ER  -