apache/spark — pull request #131 by mengxr (2014-03-13 01:22:58+00:00)
Title: [SPARK-1237, 1238] Improve the computation of YtY for implicit ALS

Computing YtY can be implemented using BLAS's DSPR operations instead of generating y_i y_i^T and then combining them. The latter generates many k-by-k matrices. On the movielens data, this change improves the performance by 10-20%. The algorithm remains the same, verified by computing RMSE on the movielens data.

To compare the results, I also added an option to set a random seed in ALS.

JIRA:
1. https://spark-project.atlassian.net/browse/SPARK-1237
2. https://spark-project.atlassian.net/browse/SPARK-1238