Modular Forms for \(\mathrm{GL}(r, \mathbb{F}_{q}[T])\): \(t\)-expansions of the basic forms

Abstract

We give closed formulas for the first few expansion coefficients of the basic modular forms for \(\mathrm{GL}(r, \mathbb{F}_{q}[T])\). Here the rank \(r\) is larger or equal to \(3\), and the forms in question include the coefficient forms \(g_{1}, \dots, g_{r}\) and the Eisenstein series \(E_{q^{i}-1}\) (\(i \in \mathbb{N}\)).