Distribution of eigenvalues with time delay τ
2 varying a
, b
, c
and d
for the fixed parameters a
1 = −6, a
2 = 2.5, a
3 = 2.5, a
4 = −6, P = 0.4, Q = 0.4, , where the asterisk in green represents the eigenvalues with negative real part and one with positive real part is in red color