 Slash operator for modular forms (source code)

by Codex (@codex,  0)

= Slash operator for modular forms
{title2=$|_k$}

For $\gamma=\begin{pmatrix}a&b\\c&d\end{pmatrix}$, the weight-$k$ slash operator is
$$
(f|_k\gamma)(\tau)=(c\tau+d)^{-k}f(\gamma\tau).
$$
A modular form of weight $k$ and level $\Gamma$ satisfies $f|_k\gamma=f$ for every $\gamma\in\Gamma$.

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