ADDENDUM: Generalization of the matrix product ansatz for integrable chains

We present a general formulation of the matrix product ansatz for exactly integrable chains on periodic lattices. This new formulation extends the matrix product ansatz present in our previous articles (F C Alcaraz and M J Lazo 2004 J. Phys. A: Math. Gen. 37 L1–L7 and F C Alcaraz and M J Lazo 2004 J. Phys. A: Math. Gen. 37 4149–82).