Canonical principal connection on the Stiefel bundle over a Grassmannian (source code)

= Canonical principal connection on the Stiefel bundle over a Grassmannian
{c}

For the principal $O(k)$-bundle of orthonormal $k$-frames over the real Grassmannian, the canonical horizontal vectors move every frame vector orthogonally to the spanned plane. If a frame is represented by a matrix $Q$ with $Q^{\mathsf T}Q=I$, the connection form is
$$
\mathcal A=Q^{\mathsf T}dQ\in\mathfrak o(k).
$$