Problem. Determine if it is true or false :
If the columns of a $n\times p$ matrix $U$ are orthonormal, then $UU^t y$ is the orthogonal projection of the vector $y$ onto the column space of $U$.
Hi, can someone tell me the theorem about this? I would like to Google it myself but i dont know how.
So someone who can explain me this or know what terms I have to Google for in Google?