Github user vrilleup commented on a diff in the pull request:
https://github.com/apache/spark/pull/964#discussion_r13418117
--- Diff:
mllib/src/main/scala/org/apache/spark/mllib/linalg/distributed/RowMatrix.scala
---
@@ -201,6 +201,19 @@ class RowMatrix(
}
/**
+ * Multiply the Gramian matrix `A^T A` by a Vector on the right.
+ *
+ * @param v a local vector whose length must match the number of columns
of this matrix
+ * @return a local DenseVector representing the product
+ */
+ private[mllib] def multiplyGramianMatrix(v: Vector): Vector = {
+ val bv = rows.map{
+ row => row.toBreeze * row.toBreeze.dot(v.toBreeze)
--- End diff --
changed to use aggregrate and axpy (from breeze). There are still some
boxing/unboxing overhead from/to breeze objects. I can further improve if
needed.
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