[SPARK-9788] [MLLIB] Fix LDA Binary Compatibility

1. Add “asymmetricDocConcentration” and revert docConcentration changes. If the (internal) doc concentration vector is a single value, “getDocConcentration" returns it. If it is a constant vector, getDocConcentration returns the first item, and fails otherwise.
2. Give `LDAModel.gammaShape` a default value in `LDAModel` concrete class constructors.

jkbradley

Author: Feynman Liang <fliang@databricks.com>

Closes #8077 from feynmanliang/SPARK-9788 and squashes the following commits:

6b07bc8 [Feynman Liang] Code review changes
9d6a71e [Feynman Liang] Add asymmetricAlpha alias
bf4e685 [Feynman Liang] Asymmetric docConcentration
4cab972 [Feynman Liang] Default gammaShape

1 files changed, 2 insertions, 2 deletions

diff --git a/mllib/src/test/scala/org/apache/spark/mllib/clustering/LDASuite.scala b/mllib/src/test/scala/org/apache/spark/mllib/clustering/LDASuite.scala
index fdc2554ab8..ce6a8eb8e8 100644
--- a/mllib/src/test/scala/org/apache/spark/mllib/clustering/LDASuite.scala
+++ b/mllib/src/test/scala/org/apache/spark/mllib/clustering/LDASuite.scala
@@ -160,8 +160,8 @@ class LDASuite extends SparkFunSuite with MLlibTestSparkContext {
 
   test("setter alias") {
     val lda = new LDA().setAlpha(2.0).setBeta(3.0)
-    assert(lda.getAlpha.toArray.forall(_ === 2.0))
-    assert(lda.getDocConcentration.toArray.forall(_ === 2.0))
+    assert(lda.getAsymmetricAlpha.toArray.forall(_ === 2.0))
+    assert(lda.getAsymmetricDocConcentration.toArray.forall(_ === 2.0))
     assert(lda.getBeta === 3.0)
     assert(lda.getTopicConcentration === 3.0)
   }