function used for RPs are:</p><p class="math-container">\[\mathbf{R}_{i,j} = \Theta(\varepsilon - \|\mathbf{x}_i - \mathbf{x}_j\|),\]</p><p>where <span>$\Theta$</span> is the Heaviside function, <span>$\|\cdot\|$</span> denotes an appropriate norm, and <span>$\varepsilon$</span> is  a threshold parameter that defines the maximum distance between two points for them to be considered <span>$\varepsilon$</span>-recurrent to each other. However, there are several variations that can be used as recurrence functi