This example shows an adjacency matrix visualizing co-occurrence weights between 43 topics, with each cell’s opacity encoding the edge weight from a CSV edge list. The code builds a square matrix of all possible source–target pairs, fills in weights from the edge hash, and renders them as SVG rectangles using D3 v3’s `d3.scale.linear` for opacity scaling. It adds row and column axes with `d3.svg.axis`, and a mouseover handler highlights entire rows and columns. The data comes from `edgelist.csv` and `nodelist.csv`, loaded via `queue().defer(d3.csv)`.