[1] Univ Nacl Autonoma Mexico, Dept Matemat & Mecan, Inst Invest Matemat Aplicadas & Sistemas, Mexico City 04510, DF, Mexico
[2] Univ Autonoma Chapingo, Dept Preparatoria Agr, Area Fis, Km 38-5 Carretera Mexico Texcoco, Texcoco 56230, Estado De Mexic, Mexico
[3] Univ Nacl Autonoma Mexico, Inst Astron, AP 70-264, Mexico City 04510, DF, Mexico