  We construct two sets of representations of the Dirac equation. They
transform themselves from one to another in multiplying by the tensor
commutation matrix (TCM) $2\otimes 2$. The Gauss matrix can lead us to the
Cholesky decomposition. The TCMs can be used in order to obtain different
transforms of some matrix equations to linear matrix equations of the form
$AX=B$. A TCM $n\otimes n$ is expressed in terms of the $n\otimes n$-Gell-Mann
matrices. In order to generalize this expression to which of TCMs $n\otimes p$,
we introduced what we call rectangle Gell-Mann matrices. The electric charge
operator (ECO) for eight leptons and quarks of the Standard Model (SM) of a
same generation proposed by Zenczykowski is expressed in terms of the TCM
$2\otimes 2$. An ECO including all the fermions of the SM is constructed in
terms of TCM $4\otimes 4$. Then the eigenvalues of a TCM take sense.
