1. Department of Mathematics, Babeş-Bolyai University, Kogălniceanu Street No. 1, 400084 Cluj-Napoca, Romania
2. Academy of Romanian Scientists, Ilfov Street No. 3, 50044 Bucharest, Romania
3. Department of Business, Babeş-Bolyai University Cluj-Napoca, Horea Street No. 7, 400174 Cluj-Napoca, Romania
4. The Key Laboratory of Intelligent Information and Big Data Processing of NingXia Province, Health Big Data Research Institute, North Minzu University, Yinchuan 750021, China