1. Department of Mathematics and Theoretical InformaticsFaculty of Electrical Engineering and InformaticsTechnical University of KošiceB. Němcovej 32 042 00 Košice Slovakia
2. Department of Engineering MathematicsFaculty of EngineeringCairo UniversityOrman Giza 12221 Egypt
3. School of Control Science and EngineeringShandong UniversityJinan Shandong 250061 P. R. China