function slack(graph, u, v, minLen) {
  return Math.abs(graph.node(u).rank - graph.node(v).rank) - minLen;
}
function slack(graph, u, v, minLen) {
  return Math.abs(graph.node(u).rank - graph.node(v).rank) - minLen;
}
function slack ( graph , u , v , minLen ) { return Math . abs ( graph . node ( u ) . rank - graph . node ( v ) . rank ) - minLen ; }
/*
A helper to calculate the slack between two nodes (`u` and `v`) given a
`minLen` constraint. The slack represents how much the distance between `u`
and `v` could shrink while maintaining the `minLen` constraint. If the value
is negative then the constraint is currently violated.

This function requires that `u` and `v` are in `graph` and they both have a
`rank` attribute.
/ * A helper to calculate the slack between two nodes ( u and v ) given a minLen constraint . The slack represents how much the distance between u and v could shrink while maintaining the minLen constraint . If the value is negative then the constraint is currently violated .