#### Vol. 1, No. 1, 2013

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Haberland's formula and numerical computation of Petersson scalar products

### Henri Cohen

Vol. 1 (2013), No. 1, 249–270
##### Abstract

We study several methods for the numerical computation of Petersson scalar products, and in particular we prove a generalization of Haberland’s formula to any subgroup of finite index $G$ of $\Gamma ={PSL}_{\mathfrak{2}}\left(ℤ\right)$, which gives a fast method to compute these scalar products when a Hecke eigenbasis is not necessarily available.