[GitHub] 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.

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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_r249496182
 
 

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 File path: mllib/src/main/scala/org/apache/spark/mllib/clustering/PowerIterationClustering.scala
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 @@ -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) {
 
 Review comment:
   Done.

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