1. M. Abramowitz, and I. A. Stegun . 1968 . Handbook of Mathematical Functions . Dover Publications, Inc., New York. p.231 .
2. C. T. Bathala, Ramachandra Rao, and J. A. Spooner . 1977 . Application of linear systems analysis to ground-water evaluation studies . Purdue University Water Resources Research Center Technical Report 91. 128 pp.