# Properties

 Label 21.2.B.d2 Name $$\mathrm{U}(1)[D_{2}]$$ Weight $21$ Degree $2$ Real dimension $1$ Components $4$ Contained in $$\mathrm{U}(2)$$ Identity component $$\mathrm{U}(1)$$ Component group $$D_{2}$$

## Invariants

 Weight: $21$ Degree: $2$ $\mathbb{R}$-dimension: $1$ Components: $4$ Contained in: $\mathrm{U}(2)$ Rational: yes

## Identity component

 Name: $\mathrm{U}(1)$ $\mathbb{R}$-dimension: $1$ Description: $\left\{\begin{bmatrix}\alpha&0\\0&\bar\alpha\end{bmatrix}:\alpha\bar\alpha = 1,\ \alpha\in\mathbb{C}\right\}$ Symplectic form: $\begin{bmatrix}0&1\\-1&0\end{bmatrix}$ Hodge circle: $u\mapsto \mathrm{diag}(u,u^{-1})$

## Component group

 Name: $D_{2}$ Order: $4$ Abelian: yes Generators: $\left\{\begin{bmatrix} 0 & 1\\ -1 & 0\end{bmatrix}, \begin{bmatrix} 1 & 0 \\ 0 & \zeta_{2}\end{bmatrix}\right\}$

## Moment sequences

$x$ $\mathrm{E}[x^{0}]$ $\mathrm{E}[x^{1}]$ $\mathrm{E}[x^{2}]$ $\mathrm{E}[x^{3}]$ $\mathrm{E}[x^{4}]$ $\mathrm{E}[x^{5}]$ $\mathrm{E}[x^{6}]$ $\mathrm{E}[x^{7}]$ $\mathrm{E}[x^{8}]$ $\mathrm{E}[x^{9}]$ $\mathrm{E}[x^{10}]$ $\mathrm{E}[x^{11}]$ $\mathrm{E}[x^{12}]$
$a_1$ $1$ $0$ $1$ $0$ $3$ $0$ $10$ $0$ $35$ $0$ $126$ $0$ $462$