1. Wong Chia-ho, Extended graphical representation of polynomials with applications to cybernetics,Applied Mathematics and Mechanics,2, 3 (1981).
2. Yuan Zhao-ding and Bi De-hua, The calculation method of root loci,Applied Mathematics and Calculation Mathematics, I, 1 (1964), 13–17. (in Chinese)
3. Goldberg, J. H., Automatic Controls: Principles of System Dynamics, Allyn and Bacon, Inc., Boston (1964). 235.
4. Tsien, H. S.,Engineering Cybernetics, McGraw-Hill Publishing Company Ltd, (1958), 88.
5. Evans, W. R.,Trans AIEE, 67 (1948), 547–551.