Douglas J. J., Rachford H. H.On the numerical solution of heat conduction problems in two and three space variables // Trans. Amer. Math. Soc., 1956, v. 82, p. 421 - 439.
Peaceman D., Rachford H.The numerical solution of parabolic and elliptic differential equations // SIAM. - 1955. - V.3, p. 28 - 41.