This function transform a fd object into a function. It require either the fd object OR the coefficient and the basis object.
Examples
basis = create_bspline_basis(0, 100, 10, 4)
coef = c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
func_from_fd = from_fd_to_func(coef = coef, basis = basis)
