Major Description
ML Evaluator currently requires that metrics be maximized (bigger is better). That is counterintuitive for some metrics. Currently, we hackily negate some metrics in RegressionEvaluator, which is weird. Instead, we should:
- Return the metric as expected (e.g., "rmse" should return RMSE, not its negation).
- Provide an indicator of whether the metric should be maximized or minimized.
Model selection algorithms can use the indicator as needed.
