1. See, for example,Guillemin, E. A.,Introductory Circuit Theory, John Wiley, New York (1953).
2. Sokolnikoff, I. S.,Mathematical Theory of Elasticity, McGraw-Hill, New York (1956), Chapter 7.
3. Toupin, R. A.,A Variational Principle for the Mesh-Type Analysis of a Mechanical System, Trans. ASME, J. appl. Mech.74, 151–152 (1952).
4. Crandall, S. H.,Complementary Extremum Principles for Dynamics Ninth International Congress of Applied Mechanics, Brussels (1956).
5. Karnopp, B. H.,Complementary Variational Principles in Linear Elastodynamics, Tensor New Series17/3, 300–307 (1966).