1. K. S. Narendra and A. M. Annaswamy, Stable Adaptive Systems. Prentice-Hall. Englewood Cliffs, NJ, USA, 1989.
2. K. S. Narendra and J. H. Taylor, Frequency domain criteria for absolute stability. Academic Press. New York, NY, USA, 1973.
3. J. Garloff and D. Wagner. Hadamard products of stable polynomials are stable. Journal of mathematical analysis and applications, 202:797-809, 1996.
4. S. P. Battacharyya, H. Chapellat, and L. H. Kell. Robust Control: The Parametric Approach. Prentice-Hall, New York, NY, USA, 1995.
5. A. Aleman, D. Beliaev, and H. Hedenmalm. Real zero polynomials and Pólya-Schur type theorems. J. Anal. Math., 94:49-60, 2004.