code: def save(self, sc, path):
          
          java_boundaries = _py2java(sc, self.boundaries.tolist())
          java_predictions = _py2java(sc, self.predictions.tolist())
          java_model = sc._jvm.org.apache.spark.mllib.regression.IsotonicRegressionModel(
              java_boundaries, java_predictions, self.isotonic)
          java_model.save(sc._jsc.sc(), path)
docs: Save an IsotonicRegressionModel.