repulsiveforce
  The power of the repulsive force used in an extended Fruchterman-Reingold
type: double, default: 1.0, minimum: 0.0
force directed model. Values larger than 1 tend to reduce
the warping effect at the expense of less clustering.
Valid on:
  Note:
  sfdp only.
  Search the Graphviz codebase for "repulsiveforce"