docs: private ProjectedEnergy projectedEnergy(Relation<V> relation, ORCLUSCluster c_i, ORCLUSCluster c_j, int i, int j, int dim) {
      NumberVectorDistanceFunction<? super V> distFunc = SquaredEuclideanDistanceFunction.STATIC;
      // union of cluster c_i and c_j
      ORCLUSCluster c_ij = union(relation, c_i, c_j, dim);
  
      double sum = 0.;
      NumberVector c_proj = DoubleVector.wrap(project(c_ij, c_ij.centroid));
      for(DBIDIter iter = c_ij.objectIDs.iter(); iter.valid(); iter.advance()) {
        NumberVector o_proj = DoubleVector.wrap(project(c_ij, relation.get(iter).toArray()));
        sum += distFunc.distance(o_proj, c_proj);
      }
      sum /= c_ij.objectIDs.size();
  
      return new ProjectedEnergy(i, j, c_ij, sum);
    }