Take the negative instead of reciprocal.

Author: viirya

mllib/src/main/scala/org/apache/spark/ml/evaluation/RegressionEvaluator.scala

@@ -70,13 +70,13 @@ final class RegressionEvaluator(override val uid: String)
     val metrics = new RegressionMetrics(predictionAndLabels)
     val metric = $(metricName) match {
       case "rmse" =>
-        1 / metrics.rootMeanSquaredError
+        -metrics.rootMeanSquaredError
       case "mse" =>
-        1 / metrics.meanSquaredError
+        -metrics.meanSquaredError
       case "r2" =>
         metrics.r2
       case "mae" =>
-        1 / metrics.meanAbsoluteError
+        -metrics.meanAbsoluteError
     }
     metric
   }

mllib/src/test/scala/org/apache/spark/ml/evaluation/RegressionEvaluatorSuite.scala

@@ -58,14 +58,14 @@ class RegressionEvaluatorSuite extends SparkFunSuite with MLlibTestSparkContext
 
     // default = rmse
     val evaluator = new RegressionEvaluator()
-    assert(evaluator.evaluate(predictions) ~== 0.1019382 absTol 0.001)
+    assert(evaluator.evaluate(predictions) ~== -0.1019382 absTol 0.001)
 
     // r2 score
     evaluator.setMetricName("r2")
     assert(evaluator.evaluate(predictions) ~== 0.9998196 absTol 0.001)
 
     // mae
     evaluator.setMetricName("mae")
-    assert(evaluator.evaluate(predictions) ~== 0.08036075 absTol 0.001)
+    assert(evaluator.evaluate(predictions) ~== -0.08036075 absTol 0.001)
   }
 }