Fuzzy Model, Neural Network and Empirical Model for the Estimation of Global Solar Radiation for Port-Harcourt, Nigeria - Akinnawo, Olumide Olufemi; Adebayo, Oluwaseun Caleb; Usifo, Abel Giwa; Ogundele, Abiodun Kazeem (Theory and Applications of Mathematical Science Vol. 1, 2020)