/**
 * Initialize the link force algorithm and start simulation.
 */
function startLinkSimulation() {
  console.log("startLinkSimulation")
  springForce = false;
  simulation.stop();
  p1 = performance.now();
  let links = [];

  // Initialize link array.
  nodes = simulation.nodes();
  for (i = 0; i < nodes.length; i++) {
    for (j = 0; j < nodes.length; j++) {
      if (i !== j) {
        links.push({
          source: nodes[i],
          target: nodes[j],
        });
      }
    }
  }

  // Add the links to the simulation.
  simulation.force(forceName, d3.forceLink().links(links));

  simulation
    .alphaDecay(1 - Math.pow(0.001, 1 / ITERATIONS))
    .force(forceName)
    // The distance function that will be used to calculate distances
    //  between nodes.
    .distance(function (n) {
      return distanceFunction(n.source, n.target, props, norm);
    })
    // Set the parameter for the algorithm (optional).
    .strength(1);
  // Restart the simulation.
  simulation.alpha(1).restart();
}