Controlling chaos by a modified straight-line stabilization method

By adjusting external control signal, rather than some available parameters of the system, we modify the straight-line stabilization method for stabil izing an unstable periodic orbit in a neighborhood of an unstable fixed poi nt formulated by Ling Yang et al., and derive a more simple analytical expr ession of the external control signal adjustment. Our technique solves the problem that the unstable fixed point is independent of the system paramete rs, for which the original straight-line stabilization method is not suitab le. The method is valid for controlling dissipative chaos, Hamiltonian chao s and hyperchaos, and may be most useful for the systems in which it may be difficult to find an accessible system parameter in some cases. The method is robust under the presence of weak external noise.