1. Department of Mathematics and Computer Science, North University Center at Baia Mare, Victorie1 76, 430122 Baia Mare , Romania
2. Department of Mathematics and Statistics, King Fahd University of Petroleum and Minerals, Dhahran , Saudi Arabia
3. Department of Statistics, Analysis, Forecast and Mathematics, Faculty of Economics and Bussiness Administration, Babeş-Bolyai University of Cluj-Napoca, Cluj-Napoca Romania