Symplectic group (awaiting review)

The real symplectic group of degree $g$ denoted by $\Sp(2g,\R)$ is defined as \[ \Sp(2g,\R) =\left\{ \gamma=\left(\begin{matrix} a & b\\ c & d\end{matrix}\right)\in\GL(2g,\R): \, \gamma^t J \gamma=J\right\}, \] where $J=\left(\begin{matrix}0 & 1_g\\ -1_g & 0\end{matrix}\right)$ with $1_g$ is the identity matrix of size $g$.

By using the following two properties of the Pfaffian: $\text{Pf}(\gamma^t J \gamma)=\text{Pf}(J)$ and $\text{Pf}(\gamma^t J \gamma)=\det(\gamma)\text{Pf}(J)$, we see that $\Sp(2g,\R)$ is a subgroup of $\SL(2g,\R)$.

The integral symplectic group $\Gamma_g=\Sp(2g,\Z)$, also called the Siegel modular group, is defined as $\Gamma_g=\Sp(2g,\R)\cap{\rm M}(2g,\Z)$. Clearly $\Gamma_1=\SL(2,\Z)$.