Unit-vector stabilizer in a special orthogonal group
= Unit-vector stabilizer in a special orthogonal group
{title2=$S_v$}
For $v\in S^n$, the stabilizer $S_v=\{R\in SO(n+1):Rv=v\}$ is conjugate to the block subgroup $SO(n)$ acting on $v^\perp$. Hence it is a submanifold of dimension $n(n-1)/2$, with
$$
T_RS_v=\{RA:A^T=-A,\ Av=0\}.
$$