V. John. Scientific Computing and Applications, volume 7 of Advances in Computation: Theory and Practice, page 75+. Huntington, New York, Nova Science Publishers, Inc., (2001)
I. Babuska, A. Craig, J. Mandel, and J. Pitkäranta. BN-1105. Institute for Physical Science and Technology, Universityof Maryland, College Park, MD, (October 1989)