Matrix generators for Weil representations

Abstract

Let $r$ be an odd prime and $\mathbb{F}$ a field containing a primitive $r$th root of unity. Then for all $\ell \geq 1$, there is a faithful representation $f: \operatorname{Sp}_{2\ell}(r) \rightarrow \operatorname{GL}_{r^\ell}(\mathbb{F})$ called the Weil representation. We provide explicit matrices generating $\operatorname{Sp}_{2\ell}(r)$ in $\operatorname{GL}_{r^\ell}(\mathbb{F})$, which we have implemented in Magma. We also describe such generators for the irreducible Weil representations of $\operatorname{Sp}_{2\ell}(r)$, which are of degree $(r^{\ell} \pm 1)/2$ and arise as irreducible constituents of the Weil representations.