docs: private static double thresholdLength(double[][] matrix, int[] edges) {
      double[] lengths = new double[edges.length >> 1];
      for(int i = 0, e = edges.length - 1; i < e; i += 2) {
        lengths[i >> 1] = matrix[edges[i]][edges[i + 1]];
      }
      Arrays.sort(lengths);
      final int pos = (lengths.length >> 1); // 50%
      return lengths[pos];
    }