@Override
  public void terminate(PointCollector collector) throws Exception {
    collector.putDouble(0, integralValue); // default: 0
  }
calculate the integral or the area under the curve of input series $unit$ is the time scale for
the area calculation, chosen from 1s(second, default), 1m(minute), 1h(hour), 1d(day).
library-udf/src/main/java/org/apache/iotdb/library/dprofile/UDAFIntegral.java