Gonçalves, João N.C., M. Teresa T. Monteiro, and Helena Sofia Rodrigues. “On the Dynamics of a Viral Marketing Model With Optimal Control Using Indirect and Direct Methods”. Statistics, Optimization & Information Computing 6, no. 4 (November 2, 2018): 633-644. Accessed November 15, 2024. http://47.88.85.238/index.php/soic/article/view/20181212.