1. Southwell, R.V., Relaxation Methods in Theoretical Physics; University Press, Oxford, 1946.
2. Shortley, G., and R. Weller, J. appl. Phys.9 (1938) 334.
3. Grinter, L. E., ed., Numerical Methods of Analysis in Engineering; see especially chapters 3, 4, 5, 8, 9, 10; chapter 10 by T. J. Higgins contains a very extensive bibliography; Macmillan, 1949.
4. Courant, R., K. Friedrichs, and H. Lewy, Math. Ann.100 (1928) 32.
5. Wiener, N., and H. B. Phillips, J. Math. Phys.2 (1923) 105.