Rattanakul, Chontita http://orcid.org/0000-0002-2362-5885
Funding for this research was provided by:
Centre of Excellence in Mathematics, Thailand
Article History
Received: 9 February 2019
Accepted: 4 June 2019
First Online: 14 June 2019
Competing interests
: The author declares that they have no competing interests.