docs: private void step2primitive(DBIDRef id, DBIDArrayIter it, int n, Relation<? extends O> relation, PrimitiveDistanceFunction<? super O> distFunc, WritableDoubleDataStore m) {
      O newObj = relation.get(id);
      for(it.seek(0); it.getOffset() < n; it.advance()) {
        // M(i) = dist(i, n+1)
        m.putDouble(it, distFunc.distance(relation.get(it), newObj));
      }
    }