The block vec matrix can be used to detect not only whether a given matrix has a Kronecker
factorization of a given form, but also, if it does not, how closely it can be approximated in the
Frobenius norm by a Kronecker product. A best approximation is determined by the singular value
decomposition of the block vec matrix. For details, see [7], where the block vec matrix is called the
rearrangement matrix.
Example 4. Consider