Github user feynmanliang commented on a diff in the pull request:
https://github.com/apache/spark/pull/9229#discussion_r42796199
--- Diff: mllib/src/main/scala/org/apache/spark/ml/ann/Layer.scala ---
@@ -226,44 +236,21 @@ private[ann] trait ActivationFunction extends
Serializable {
/**
* Implements a function
- * @param x input data
- * @param y output data
*/
- def eval(x: BDM[Double], y: BDM[Double]): Unit
+ def eval: Double => Double
/**
* Implements a derivative of a function (needed for the back
propagation)
- * @param x input data
- * @param y output data
*/
- def derivative(x: BDM[Double], y: BDM[Double]): Unit
-
- /**
- * Implements a cross entropy error of a function.
- * Needed if the functional layer that contains this function is the
output layer
- * of the network.
- * @param target target output
- * @param output computed output
- * @param result intermediate result
- * @return cross-entropy
- */
- def crossEntropy(target: BDM[Double], output: BDM[Double], result:
BDM[Double]): Double
-
- /**
- * Implements a mean squared error of a function
- * @param target target output
- * @param output computed output
- * @param result intermediate result
- * @return mean squared error
- */
- def squared(target: BDM[Double], output: BDM[Double], result:
BDM[Double]): Double
+ def derivative: Double => Double
}
/**
- * Implements in-place application of functions
+ * Implements in-place application of functions in the arrays
*/
-private[ann] object ActivationFunction {
+private[ann] object UniversalFunction {
--- End diff --
I found it slightly confusing that the `apply` method of a companion object
is mutating in place since companion object `apply`s are typically used to
implement default constructors; we should consider renaming `apply` -> `call`
if you think that's clearer
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