| We give in this note some expansion formulas for the orthogonal projectors onto the range of the row block matrix $[\, A, \, B \,]$, and use the expansion formulas to examine relations among the orthogonal projectors onto the ranges of $A$, $B$ and $[\, A, \, B \,]$. In particular, we present some identifying conditions for a pair of orthogonal projectors of the same size to commute. |
