An Algorithm for Detecting Hopf-Birfucation Varieties of Nonlinear   Polynomial Systems
  An algorithm is presented here, for discovering Hopf-Bifurcation varieties of polynomial dynamical systems. It is based on the expression of specific polynomials, as sums of products of first degree polynomials, with parametrical coefficients. By giving to these parameters certain values, we ensure the positiveness of some quantities, constructing thereby proper Lyapunov functions, which guarantee the stability of the equilibrium point. The points where the afore mentioned positiveness fails, define the Hopf-Bifurcation varieties upon discussion. 
Stelios Kotsios