This example visualizes a small network of six academic subjects, grouped into three clusters, using a force-directed layout. It shows the relationships between nodes as weighted links, with line thickness proportional to the link weight and node labels displayed beside circles. The code uses `d3.layout.force` from D3 v4 to simulate the physics and positions elements in an SVG container. It loads data from a local JSON file, applies CSS styling to links and nodes, and updates positions on each tick event.