Funding for this research was provided by:
Centre of Excellence in Mathematics, Commission on Higher Education (2)
The 2018 SAE summer scholarship from the faculty of Science and Engineering (1)
Text and Data Mining valid from 2019-06-11
Received: 2 February 2019
Accepted: 27 May 2019
First Online: 11 June 2019
: The authors declare that they have no competing interests.