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arXiv · 2001.07270

Computing actions on cusp forms

David Zywina
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Abstract

For positive integers $k$ and $N$, we describe how to compute the natural action of $SL_2(\mathbb{Z})$ on the space of cusp forms $S_k(\Gamma(N))$, where a cusp form is given by sufficiently many terms of its $q$-expansion. This will reduce to computing the action of the Atkin--Lehner operator on $S_k(\Gamma)$ for a congruence subgroup $\Gamma_1(N)\subseteq \Gamma \subseteq \Gamma_0(N)$. Our motivating application of such fundamental computations is to compute explicit models of some modular curves $X_G$.

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David Zywina. 2020-01-20. Computing actions on cusp forms. https://arxiv.org/abs/2001.07270

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