title: Spring Forces in D3.js Force directed layout?
body: <p>The description of this example: <a href="http://bl.ocks.org/mbostock/4062045" rel="nofollow noreferrer">http://bl.ocks.org/mbostock/4062045</a> (find image below), states that it is "A physical simulation of charged particles and springs places related characters in closer proximity." </p>
  
  <p><img src="https://i.stack.imgur.com/a6aXl.gif" alt="enter image description here"></p>
  
  <p>I was just curious which part of that code (on that same page) implements or defines the spring forces, especially based on related characters?</p>
  
  <p>I ask this because i was under the impression that D3.js does not implement spring forces for the Force directed layouts, as mentioned in its API documentation: </p>
  
  <p>"Links are not implemented as "spring forces", as in common in other force-directed layouts, but as weak geometric constraints." -<a href="https://github.com/mbostock/d3/wiki/Force-Layout#wiki-linkDistance" rel="nofollow noreferrer">https://github.com/mbostock/d3/wiki/Force-Layout#wiki-linkDistance</a></p>