On the Computation of the Third Order Terms of the Series Defining the Center Manifold for a Scalar Delay Differential Equation

When computing the third order terms of the series of powers of the function whose graph is the center manifold, at an equilibrium point of a scalar delay differential equation with a single constant delay r > 0, some problems occur at the term w_2,1z²`(z)].{w_{2,1}z^2\overline{z}.} More precisely, in order to determine the values at 0, respectively −r of the function w _2,1(.), an algebraic system of equations must be solved. We show that the two equations are dependent, hence the system has an infinity of solutions. Then we show how we can overcome this lack of uniqueness and provide a formula for w _2,1(0).