1. Statistics and Mathematics Research, Centre (InAEM), Escuela Superior, Politécnica de Chimborazo, Riobamba, Ecuador, Faculty of Science, Panamericana, Sur, Riobamba, Ecuador
2. University of Salamanca, Salamanca, Spainm, Faculty of Science, Plaza de los, Caídos S/N, Salamanca, Spain
3. University of León, León, Spain, Escuela de Ingenierías, Campus de, Vegazana S/N, León, Spain