Funding for this research was provided by:
Fundação para a Ciência e a Tecnologia (UID/MAT/00297/2019)
Fundação para a Ciência e a Tecnologia (UID/MAT/00212/2019.)
Article History
Received: 13 September 2018
Accepted: 6 June 2019
First Online: 19 June 2019