Wangrat, S.
Niamsup, P. http://orcid.org/0000-0003-2616-8605
Funding for this research was provided by:
Center of Excellence in Mathematics, Thailand
Chiang Mai University, Thailand
Article History
Received: 4 September 2017
Accepted: 20 March 2018
First Online: 11 April 2018
Competing interests
: The authors declare that they have no competing interests.