J(𝐱,𝐲)=|𝐱∩𝐲||𝐱∪𝐲|=#non-zero entries in common#non-zero entries in totalJ(\mathbf{x},\mathbf{y})=\frac{|\mathbf{x} \cap \mathbf{y}|}{|\mathbf{x} \cup \mathbf{y}|}=\frac{\textrm{\# non-zero entries in common}}{\textrm{\# non-zero entries in total}}