@Override
  public void transform(Row row, PointCollector collector) throws Exception {
    if (!row.isNull(0)
        && !row.isNull(1)
        && Double.isFinite(Util.getValueAsDouble(row, 0))
        && Double.isFinite(Util.getValueAsDouble(row, 1))) {
      time.add((int) row.getTime());
      real.add(Util.getValueAsDouble(row, 0));
      imag.add(Util.getValueAsDouble(row, 1));
    }
  }
This function does Inverse Fast Fourier Transform for input series.
library-udf/src/main/java/org/apache/iotdb/library/frequency/UDTFIFFT.java