For cubic differential systems with two homogeneous invariant straight lines and one invariant conic, it is proved that a singular point with pure imaginary eigenvalues (a weak focus) is a centre if and only if the fi...For cubic differential systems with two homogeneous invariant straight lines and one invariant conic, it is proved that a singular point with pure imaginary eigenvalues (a weak focus) is a centre if and only if the first two Lyapunov quantities Lj , j = 1, 2 vanish.展开更多
文摘For cubic differential systems with two homogeneous invariant straight lines and one invariant conic, it is proved that a singular point with pure imaginary eigenvalues (a weak focus) is a centre if and only if the first two Lyapunov quantities Lj , j = 1, 2 vanish.
