Github user srowen commented on a diff in the pull request:
https://github.com/apache/spark/pull/18022#discussion_r117192700
--- Diff: mllib/src/main/scala/org/apache/spark/ml/recommendation/ALS.scala
---
@@ -763,11 +763,15 @@ object ALS extends DefaultParamsReadable[ALS] with
Logging {
/**
* Representing a normal equation to solve the following weighted least
squares problem:
*
- * minimize \sum,,i,, c,,i,, (a,,i,,^T^ x - b,,i,,)^2^ + lambda * x^T^ x.
+ * minimize \sum,,i,, c,,i,, (a,,i,,^T^ x - d,,i,,)^2^ + lambda * x^T^ x.
*
* Its normal equation is given by
*
- * \sum,,i,, c,,i,, (a,,i,, a,,i,,^T^ x - b,,i,, a,,i,,) + lambda * x =
0.
+ * \sum,,i,, c,,i,, (a,,i,, a,,i,,^T^ x - d,,i,, a,,i,,) + lambda * x =
0.
+ *
+ * Distributing and letting b,,i,, = d,,i,, * b,,i,,
--- End diff --
I'm not clear on this change. It defines $b_i$ in terms of itself? what is
this correcting?
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