Next, they state the idea of a physical threshold $Q$ so that only pairs of nodes with a link strength greater than $Q$ will be regarded as significantly linked.

To this end, they define a new matrix, that takes on the value 1 whenever two nodes are significantly linked, otherwise it is 0:

$ \rho(\ell,r,y) = \Theta(W(\ell,r,y) - Q) $

where $\Theta$ is the Heaviside function, mapping negative values to 0, positives values to 1 (and 0 to 0.5).