1. Department of Mathematics and Statistics, Lamar University, Beaumont, TX 77710, USA
2. Scientific Computing Group, Universidad de Salamanca, Plaza de la Merced, Salamanca 37008, Spain
3. Escuela Politécnica Superior de Zamora, Campus Viriato, Zamora 49022, Spain
4. Mathematics Programme, National Mathematical Centre, Abuja, Nigeria
5. Department of Mathematics, University of Abuja, Nigeria