content_image/303847.jpg content_image/303845.jpg content_image/303846.jpg
On the other hand, according to the Pyragas control method [27, 43], an unstable periodic solution with period τ$_{0}$ can be stabilized by using an external perturbation of the form C [ s ( t − τ$_{0}$ ) − s ( t )] , where C is the strength of the perturbation, s ( t ) is a scalar signal which is given by some function of the state of the system and s ( t − τ$_{0}$ ) is the signal measured with a time delay equal to τ$_{0}$. 

To stabilize an unstable quasi-periodic solution of (4.26), we construct the following control system, 

<img src='content_image/303847.jpg'>

We make use of the OGY control method around the fixed point 2 . 9 / 3 . $_{9}$of the logistic map (4.22) so that 

<img src='content_image/303845.jpg'>

<img src='content_image/303846.jpg'>

¯ λ$_{j}$ in (4.28) is given by the formula (4.27) in which κ ( i ) ≡ 2 . 9 / 3 . $_{9}$. The control mechanism is switched on 

