public static double popVariance(List<Double> data) {
    double variance = 0;
    for (int i = 0; i < data.size(); i++) {
      variance = variance + (Math.pow((data.get(i) - mean(data)), 2));
    }
    variance = variance / data.size();
    return variance;
  }
calculate pop variance of list

@param data need to calculate list
@return pop variance of list
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/utils/MathUtils.java