code: public double calculateAUCPR() {
          if (auprc != null) {
              return auprc;
          }
  
          if (exampleCount == 0) {
              return Double.NaN;
          }
  
          auprc = getPrecisionRecallCurve().calculateAUPRC();
          return auprc;
      }
docs: Calculate the area under the precision/recall curve - aka AUCPR
  
  @return