[1] Univ Carlos III Madrid, Escuela Politecn Super, Dept Matemat, Laganes Madrid 28911, Spain
[2] Univ Almeris, Dept Estadist & Matemat Aplicada, La Canada De San Urbano 04120, Almeria, Spain
[3] Univ Granada, Inst Carlos Fis Teor & Computac 1, E-18071 Granada, Spain