Squared Euclidean norm
= Squared Euclidean norm
{title2=$\|v\|_2^2=v\cdot v$}
For a real vector $v$, the square of its <Euclidean norm> is $\|v\|_2^2=v\cdot v=\sum_jv_j^2$. Unlike the norm itself it is a quadratic function, so expanding sums directly exposes diagonal and cross terms. This is useful for the <mean-square displacement of an isotropic planar random walk>.