Fig. 3.

Representation of the eigenvalues solutions of Eq. (11) in the complex plane (Real $(\lambda )$, Imag $(\lambda )$) for $0.001\le k_1\le 0.08$, $0.0003\le k_2\le 0.001$, while keeping $I_1=0.74,I_2=0.02,f_1=0.04$ and $f_2=0.01$. Provided that J_e is a real matrix, complex eigenvalues occur in complex conjugate pairs responsible of the symmetry observed along the real axis. The locus intersects the imaginary axis and thus suggests the possibility of Hopf bifurcation