src/sankeyCircular.js
function circularLinksCross (link1, link2) {
    if (link1.source.column < link2.target.column) {
      return false
    } else if (link1.target.column > link2.source.column) {
      return false
    } else {
      return true
    }
  }
function circularLinksCross (link1, link2) {
    if (link1.source.column < link2.target.column) {
      return false
    } else if (link1.target.column > link2.source.column) {
      return false
    } else {
      return true
    }
  }
Check if two circular links potentially overlap