I am not sure how to interpret the $\times$ symbol in the below usage:
$$2\lfloor e\times \rfloor$$ where $e = \begin{bmatrix}0 & 1 & 0\end{bmatrix}^T$
Note that the $\times$ here, is not a variable of course, but a symbol.
(This is part of a bigger equation but I am omitting it now to simplify the question)
Update 1
After "staring" at the equation for some time, I realized that the authors are using the above representation, i.e. $\lfloor e\times \rfloor$ to symbolize a $3\times3$ skew symmetric matrice! That is $[e]_\times$.
Thanks!