docs: private DoubleDBIDList initialRange(DBIDRef obj, DBIDs cands, PrimitiveDistanceFunction<? super NumberVector> df, double eps, KernelDensityEstimator kernel, ModifiableDoubleDBIDList n) {
      n.clear();
      NumberVector o = kernel.relation.get(obj);
      final double twoeps = eps * 2;
      int matches = 0;
      for(DBIDIter cand = cands.iter(); cand.valid(); cand.advance()) {
        final double dist = df.distance(o, kernel.relation.get(cand));
        if(dist <= twoeps) {
          n.add(dist, cand);
          if(dist <= eps) {
            ++matches;
          }
        }
      }
      n.sort();
      return n.slice(0, matches);
    }