shahidki31 commented on a change in pull request #21627:
[SPARK-24484][MLLIB]Power Iteration Clustering is giving incorrect clustering
results when there are mutiple leading eigen values.
URL: https://github.com/apache/spark/pull/21627#discussion_r249497213
##########
File path:
mllib/src/main/scala/org/apache/spark/mllib/clustering/PowerIterationClustering.scala
##########
@@ -378,6 +378,22 @@ object PowerIterationClustering extends Logging {
logInfo(s"$msgPrefix: delta = $delta.")
diffDelta = math.abs(delta - prevDelta)
logInfo(s"$msgPrefix: diff(delta) = $diffDelta.")
+
+ if (math.abs(diffDelta) < tol) {
+ /**
+ * Power Iteration fails to converge if absolute value of top 2 eigen
values are equal,
+ * but with opposite sign. The resultant vector flip-flops between two
vectors.
+ * We should give an exception, if we detect the failure of the
convergence of the
+ * power iteration
+ */
+ val reileigh = curG.joinVertices(v) {
+ case (_, x, y) => x * y
+ }.vertices.values.sum() / curG.vertices.mapValues(x => x *
x).values.sum()
+
+ if (math.abs(norm - math.abs(reileigh)) > tol) {
+ throw new SparkException("Power Iteration fail to converge")
Review comment:
Yes. I would like to know, instead of throwing exception, can we just print
log error stating that it is failed to converge? But, in that case, we can't
write UT.
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