References
- Araki , M. and Kondo , B. 1972 . IEEE Trans. Auto. Contr. AC . 17 : 537 – 541 .
- Barbalat , I. 1959 . Rev. Roumaine Math. . 4 : 267 – 270 .
- Cushing , J.M. 1977 . SIAM. J. Appl. Math. . 32 ( 1 ) : 82 – 95 .
- Gopalsamy , K. 1985 . Tohoku Math J. . 37 : 323 – 332 .
- Halanay , A. 1966 . “ Differential equations: stability ” . In oscillations and time lags , Vol. 23 , New York : Academic Press .
- Ma , Z. and Wang , W. 1989 . Appl. Anal. . 34 : 79 – 90 .
- Yoshizawa , T. 1975 . “ Stability theory and the existence of periodic solutions and almost periodic solutions ” . In Appl. Math. Sci. , Vol. 14 , Springer—Verlag .