“…Orthogonal basis functions have been generally used to achieve approximate solution for many problems in various fields of science. Approximation of the solution using these functions is known as a useful tool in solving many classes of equations numerically, for example, differential equations (Ganji et al, 2020a; Jafari et al, 2019; Sadeghi et al, 2020), partial differential equations (Tajadodi, 2020; Tuan et al, 2020b), integro-differential equations (Ganji et al, 2020b; Jafari et al, 2021; Tuan et al, 2020a), and FOCPs (Heydari et al, 2020; Lotfi et al, 2011; Nemati, 2016) of various orders (fixed, fractional, or variable order).…”