1) M. Araki: Stability of Large-Scale Nonlinear Systems-Quadratic-Order Theory of Composite-System Method Using M-Matrices, IEEE Trans. on Automatic Control, AC-23-2, 129/142 (1978)
2) M. Araki: Input-Output Stability of Composite Feedback Systems, IEEE Trans. on Automatic Control, AC-21-5, 254/259 (1976)
3) S. Weissenberger: Stability Regions of Large-Scale Systems, Automatica, 9-6, 653/663 (1973)
4) K. S. Narendra and J. H. Taylor: Frequency Domain Criteria for Absolute Stability, Academic Press, New York (1973)