1) G. Lüders and K.S. Narendra: Stable Adaptive Schemes for State Estimation and Identification of Linear System, IEEE Trans. on Automatic Control, AC-19-6, 841/847 (1974)
2) G. Kreisselmeier: Adaptive Observer with Exponential Rate of Convergence, IEEE Trans. on Automatic Control, AC-22-1, 2/8 (1977)