Euclidean distance

When we want to measure the dissimilarity of two vectors we can use the Euclidean distance of these. The error is then computed as the distance of two vectors we want to compare, let $\mathbf{\mu_1}$, $\mathbf{\mu_2}$ are such vectors then the error function is computed as their Euclidean distance:

$$e_{\mu_1,\mu_2} = \vert\vert \mathbf{\mu_1} - \mathbf{\mu_2} \vert\vert$$