1. School of Information , Zhejiang University of Finance & Economics Dongfang College , Jiaxing , Zhejiang 314408 , PR China
2. Department of Mathematics and Statistics , University of South Florida , Tampa , FL 33620 , USA
3. Department of Mathematics , Zhejiang Normal University , Jinhua 321004 , Zhejiang , PR China
4. Department of Mathematics , King Abdulaziz University , Jeddah , Saudi Arabia
5. College of Mathematics and Physics , Shanghai University of Electric Power , Shanghai 200090 , PR China
6. School of Mathematical and Statistical Sciences , North-West University , Mafikeng Campus, Private Bag X2046 , Mmabatho 2735 , South Africa
7. School of Mathematics and Physics , North China Electric Power University , Beijing , 102206 , PR China