^{a}Licenciatura en Matemáticas, Universidad del Quindío, Quindío, Colombia
^{b}Departamento de Matematicas, Universidad del Valle, Cali, Colombia
^{c}Mathematical, Computational and Modeling Sciences Center, Arizona State University, Tempe, AZ, USA
^{d}Department of Applied Mathematics, Kyung Hee University, Yongin, Korea
© 2014 Published by Elsevier B.V. on behalf of Korea Centers for Disease Control and Prevention.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.