$ r×(\omega×r)=(r\cdot r)\omega - (r\cdot \omega)r = |r|^2\omega - (r\cdot \omega)r = ???? = (|r|^2 I_{3\times 3} - r r^T)\omega$
These are all column vectors while $I_{3\times 3}$ is an identity matrix and $r^T$ is a row vector.
This is a step needed to prove the matrix form of the moment of inertia used here:
https://ccrma.stanford.edu/~jos/waveguide/Angular_Momentum_Vector_Matrix.html
I am interested in the mathematical steps required in the ???? symbols.
I don't understand where comes from the 3×3 identity matrix called "I" .
Here:
$\cdot$ means "dot product";
$\times$ means "cross product".
