A Definition of the Wilson action on a lattice plaquette?

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What are the terms to be calculated in the "Wilson action" definition on a Yang-Mills plaquette?
The definition of the Wilson action relating to discrete Yang-Mills model is:

$$ S_{plaq} (\sigma) := \frac{1}{2}\sum_{plaq}\|I_N - \sigma_p\|^2 $$

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(from [here] at 5:55)

It is mentioned that ##\sigma_p## is some kind of a matrix. Could anyone give an explicit example of what a ##\sigma_p## matrix look like, please?

Does the multiplication of sigmas

$$ \sigma_p = \sigma_{e1} \sigma_{e2} \sigma_{e3} \sigma_{e4} $$

mean consecutive matrix multiplication of the four square ##\sigma_e## matrices?
 
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James1238765 said:
TL;DR Summary: What are the terms to be calculated in the "Wilson action" definition on a Yang-Mills plaquette?

Does the multiplication of sigmas

$$ \sigma_p = \sigma_{e1} \sigma_{e2} \sigma_{e3} \sigma_{e4} $$

mean consecutive matrix multiplication of the four square ##\sigma_e## matrices?
In general, matrix multiplications are associative so you can multiply in whatever order works for you. However, matrix multiplcations are not commutative so you can't switch the order around at all.
 
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