@Override
  public void beforeStart(UDFParameters udfParameters, UDTFConfigurations udtfConfigurations)
      throws Exception {
    udtfConfigurations
        .setAccessStrategy(new RowByRowAccessStrategy())
        .setOutputDataType(Type.DOUBLE);
    valueArrayList0.clear();
    valueArrayList1.clear();
  }
This function calculates cross correlation between two input series.
library-udf/src/main/java/org/apache/iotdb/library/dmatch/UDTFXCorr.java