function linkAngle (link) {
    var adjacent = Math.abs(link.y1 - link.y0)
    var opposite = Math.abs(link.target.x0 - link.source.x1)

    return Math.atan(opposite / adjacent)
  }
function linkAngle (link) {
    var adjacent = Math.abs(link.y1 - link.y0)
    var opposite = Math.abs(link.target.x0 - link.source.x1)

    return Math.atan(opposite / adjacent)
  }
function linkAngle ( link ) { var adjacent = Math . abs ( link . y1 - link . y0 ) var opposite = Math . abs ( link . target . x0 - link . source . x1 ) return Math . atan ( opposite / adjacent ) }
Return the angle between a straight line between the source and target of the link, and the vertical plane of the node
Return the angle between a straight line between the source and target of the link and the vertical plane of the node