projection operator

《Advanced Linear Algebra》 · 第 73 页 · Chapter 2「Projection Operators」

Let $V=S\oplus U$. The linear operator $\rho_{S,U}:V\to V$ defined by $\rho_{S,U}(s+u)=s$, where $s\in S$ and $u\in U$, is called projection onto $S$ along $U$.