We establish Sakakibara’s differential equations [M. Sakakibara, On the differential equations of the characters for the renormalization group, Mod. Phys. Lett. A 19 (2004), 1453.] in a matrix setting for the counter term (respectively renormalized character) in Connes-Kreimer’s Birkhoff decomposition in any connected graded Hopf algebra, thus including Feynman rules in perturbative renormalization as a key example.
"On matrix differential equations in the Hopf algebra of renormalization." Adv. Theor. Math. Phys. 10 (6) 879 - 913, December 2006.