a force layout where like-nodes cluster together, drawn from static data
an iteration on the block Clustered Force Layout 4.0 from @shancarter
while es-linting code from this block, I read up on operator precendence in Javascript. It turns out that multiplication * is evaluated before division /.
check out the companion repo for a nice commit history and related experiments
https://d3js.org/d3.v4.min.js