zhengruifeng commented on a change in pull request #27758:
URL: https://github.com/apache/spark/pull/27758#discussion_r411885963
##########
File path: mllib-local/src/main/scala/org/apache/spark/ml/impl/Utils.scala
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@@ -27,4 +27,55 @@ private[ml] object Utils {
}
eps
}
+
+ /**
+ * Convert an n * (n + 1) / 2 dimension array representing the upper
triangular part of a matrix
+ * into an n * n array representing the full symmetric matrix (column major).
+ *
+ * @param n The order of the n by n matrix.
+ * @param triangularValues The upper triangular part of the matrix packed in
an array
+ * (column major).
+ * @return A dense matrix which represents the symmetric matrix in column
major.
+ */
+ def unpackUpperTriangular(
Review comment:
OK, I will look for it.
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