docs: protected static double getScore(DataSet workOn, Object evaluater, int folds, Random rand)
      {
          if(workOn instanceof ClassificationDataSet)
          {
              ClassificationModelEvaluation cme =
                      new ClassificationModelEvaluation((Classifier)evaluater, 
                      (ClassificationDataSet)workOn);
              cme.evaluateCrossValidation(folds, rand);
  
              return cme.getErrorRate();
          }
          else if(workOn instanceof RegressionDataSet)
          {
              RegressionModelEvaluation rme = 
                      new RegressionModelEvaluation((Regressor)evaluater, 
                      (RegressionDataSet)workOn);
              rme.evaluateCrossValidation(folds, rand);
              
              return rme.getMeanError();
          }
          return Double.POSITIVE_INFINITY;
      }