1. Chandrasekhar, S., Radiative Transfer, Dover, New York, 1960.
2. Preisendorfer, R. W., Radiative Transfer in Discrete Spaces, Pergamon, Oxford, 1965.
3. Redheffer, R. M., Difference Equations and Functional Equations in Transmission Line Theory, in Modern Mathematics for Engineers, (Beckenbach, Editor) Second Series, McGraw-Hill, New York, 1961.
4. Bellman, R., R. Kalaba, and M. Prestrud, Invariant Imbedding and Radiative Transfer in Slabs of Finite Thickness, American Elsevier, New York, 1963.
5. Wing, G. M., An Introduction to Transport Theory, John Wiley and Sons, New York, 1962.