Funding for this research was provided by:
Xinjiang Normal University Doctoral Research Fund (XJNUB1540)
Graduate Science and Technology Innovation Project of Xinjiang Normal University (XSY201702001)
the Science and Technology Innovation Personnel Training Project for Youth of Xinjiang (QN2016JQ0367)
Mathematics Key Subject of Xinjiang Normal University (17SDKD1106)
Article History
Received: 16 January 2018
Accepted: 1 April 2018
First Online: 6 April 2018
Competing interests
: The authors declare that they have no competing interest.