1. Department Applied Mathematics and Mathematical Analysis, Instituto de Matemática Interdisciplinar, Universidad Complutense de Madrid, Madrid 28040, Spain
2. Dept. Applied Mathematics for ICT, Universidad Politécnica de Madrid, Madrid 28031, Spain
3. Department Mathematics and Computer Sciences, Çankaya University, Ankara 06790, Turkey
4. Department Computer Architecture and Automation, Universidad Complutense de Madrid, Madrid 28040, Spain
5. Department Applied Mathematics for ICT, Universidad Politécnica de Madrid, Madrid 28040, Spain