I have a question About the eq.7 in paper

Eq7:
$\left.\Delta s=\left\{\begin{array}{cc}\Delta i_c\cdot\Delta i&\quad\text{if}|\Delta i_c\cdot\Delta i|\geq\beta\\0&\quad\text{otherwise}\end{array}\right.\right.$
In my mind, the $\Delta i_c$ is $\Delta i[c]$, that's right?
So the $\Delta i_c$ is a number, and the $\Delta i$ is a vector?
So the $\Delta i_c$，c=1,2,...,512 ?
So$\Delta s$ have 512 vector？
