A trivial example is the matrix ##A=\left(\begin{smallmatrix}0&1\\1&0\end{smallmatrix}\right)##, the square of which is the identity matrix. The identity operation is technically a projection.
#3
LagrangeEuler
711
22
I need projection matrix ##P## on the direction. So matrix for which eigenvalues are ##1## and ##0##, and for which ##TrP=1##.