class MeanWithClusterProbAggregator implements Serializable {

    MeanWithClusterProbAggregator plus(MeanWithClusterProbAggregator other) {
        return new MeanWithClusterProbAggregator(
            weightedXsSum.plus(other.weightedXsSum),
            pcxiSum + other.pcxiSum,
            rowCount + other.rowCount
        );
    }

      MeanWithClusterProbAggregator();
      MeanWithClusterProbAggregator(Vector weightedXsSum, double pcxiSum, int rowCount);

}