Code review changes

Author: Feynman Liang

mllib/src/main/scala/org/apache/spark/mllib/clustering/LDA.scala

@@ -82,9 +82,11 @@ class LDA private (
   def getAsymmetricDocConcentration: Vector = this.docConcentration
 
   /**
-   * Gets the concentration parameter, assuming the document-topic Dirichlet distribution is
-   * symmetric. Included for backwards compatibility. This method should fail if
-   * [[docConcentration]] is asymmetric.
+   * Concentration parameter (commonly named "alpha") for the prior placed on documents'
+   * distributions over topics ("theta").
+   *
+   * This method assumes the Dirichlet distribution is symmetric and can be described by a single
+   * [[Double]] parameter. It should fail if docConcentration is asymmetric.
    */
   def getDocConcentration: Double = {
     val parameter = docConcentration(0)
@@ -121,6 +123,7 @@ class LDA private (
    *       [[https://github.com/Blei-Lab/onlineldavb]].
    */
   def setDocConcentration(docConcentration: Vector): this.type = {
+    require(docConcentration.size > 0, "docConcentration must have > 0 elements")
     this.docConcentration = docConcentration
     this
   }

mllib/src/main/scala/org/apache/spark/mllib/clustering/LDAModel.scala

@@ -189,8 +189,8 @@ class LocalLDAModel private[clustering] (
     val topics: Matrix,
     override val docConcentration: Vector,
     override val topicConcentration: Double,
-    override protected[clustering] val gammaShape: Double = 100
-  ) extends LDAModel with Serializable {
+    override protected[clustering] val gammaShape: Double = 100)
+  extends LDAModel with Serializable {
 
   override def k: Int = topics.numCols
 
@@ -456,8 +456,8 @@ class DistributedLDAModel private[clustering] (
     override val docConcentration: Vector,
     override val topicConcentration: Double,
     private[spark] val iterationTimes: Array[Double],
-    override protected[clustering] val gammaShape: Double = 100
-  ) extends LDAModel {
+    override protected[clustering] val gammaShape: Double = 100)
+  extends LDAModel {
 
   import LDA._