Github user sethah commented on a diff in the pull request:
https://github.com/apache/spark/pull/17094#discussion_r103489444
--- Diff:
mllib/src/main/scala/org/apache/spark/ml/optim/aggregator/DifferentiableLossAggregator.scala
---
@@ -0,0 +1,88 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.spark.ml.optim.aggregator
+
+import org.apache.spark.ml.linalg.{BLAS, Vector, Vectors}
+
+/**
+ * A parent trait for aggregators used in fitting MLlib models. This
parent trait implements
+ * some of the common code shared between concrete instances of
aggregators. Subclasses of this
+ * aggregator need only implement the `add` method.
+ *
+ * @tparam Datum The type of the instances added to the aggregator to
update the loss and gradient.
+ * @tparam Agg Specialization of [[DifferentiableLossAggregator]]. Classes
that subclass this
+ * type need to use this parameter to specify the concrete
type of the aggregator.
+ */
+private[ml] trait DifferentiableLossAggregator[
+ Datum,
+ Agg <: DifferentiableLossAggregator[Datum, Agg]] extends Serializable {
+
+ self: Agg =>
+
+ protected var weightSum: Double = 0.0
+ protected var lossSum: Double = 0.0
+
+ /** The dimension of the gradient array. */
+ protected val dim: Int
+
+ /** Array of gradient values that are mutated when new instances are
added to the aggregator. */
+ protected lazy val gradientSumArray: Array[Double] =
Array.ofDim[Double](dim)
+
+ /** Add a single data point to this aggregator. */
+ def add(instance: Datum): Agg
+
+ /** Merge two aggregators. The `this` object will be modified in place
and returned. */
+ def merge(other: Agg): Agg = {
+ require(dim == other.dim, s"Dimensions mismatch when merging with
another " +
+ s"LeastSquaresAggregator. Expecting $dim but got ${other.dim}.")
--- End diff --
change this to use `getClass.getName`
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