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## Main Question or Discussion Point

In some text, I read something like this

[tex]\vec{S}_i\cdot\vec{S}_j[/tex]

where [tex]\vec{S}_i[/tex] and [tex]\vec{S}_j[/tex] are "vectors" with each components be the pauli matrices [tex]S_x, S_y, S_z[/tex] individularly. My question is: if all components of this kind of vector are a 3x3 matrix, so how do you carry out the dot product? So the dot product will give another matrix instead of a number?

[tex]\vec{S}_i\cdot\vec{S}_j[/tex]

where [tex]\vec{S}_i[/tex] and [tex]\vec{S}_j[/tex] are "vectors" with each components be the pauli matrices [tex]S_x, S_y, S_z[/tex] individularly. My question is: if all components of this kind of vector are a 3x3 matrix, so how do you carry out the dot product? So the dot product will give another matrix instead of a number?