Tangent space from a local parametrization (source code)

= Tangent space from a local parametrization

If $\phi:U\subseteq\mathbb R^d\to M\subseteq\mathbb R^n$ is a local parametrization with $\phi(u)=p$, then
$$
T_pM=\operatorname{im}D\phi_u.
$$
The derivative has rank $d$, so this is a $d$-dimensional vector subspace. A change of parametrization composes $D\phi_u$ with an invertible coordinate-change derivative, leaving its image unchanged.