1. Department of Mathematics and Applications; University Federico II of Naples; Complesso Monte S. Angelo Via Cintia 80126 Naples Italy
2. Center for Machine Perception; Department of Cybernetics, Faculty of Electrical Engineering, Czech Technical University in Prague; Technická 2, CZ-166 27 Prague Czech Republic
3. Department of Mathematics; Faculty of Electrical Engineering, Czech Technical University in Prague; Technická 2, CZ-166 27 Prague Czech Republic