*3.1. Anylis of Equilibria*

For system (2), the equilibria can be solved by the following equation:

$$\begin{cases} -ay - \mathbf{x}z - \mathbf{u} = \mathbf{0} \\ -c\mathbf{x} + \mathbf{x}z = \mathbf{0} \\ -b - m\mathbf{x}y = \mathbf{0} \\ k\mathbf{x} - y = \mathbf{0} \end{cases} \tag{4}$$

The fourth equation indicates that *y* = *kx*, but the third equation means that *b* = −*mxy*, then *b* = <sup>−</sup>*mkx*2, which means that there is no real solution, correspondingly the hyperchaotic attractor of system (2) is hidden.
