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Posted to issues@spark.apache.org by "Xiangrui Meng (JIRA)" <ji...@apache.org> on 2015/07/21 02:01:11 UTC
[jira] [Updated] (SPARK-9175) BLAS.gemm fails to update matrix C
when alpha==0 and beta!=1
[ https://issues.apache.org/jira/browse/SPARK-9175?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Xiangrui Meng updated SPARK-9175:
---------------------------------
Target Version/s: 1.5.0
> BLAS.gemm fails to update matrix C when alpha==0 and beta!=1
> ------------------------------------------------------------
>
> Key: SPARK-9175
> URL: https://issues.apache.org/jira/browse/SPARK-9175
> Project: Spark
> Issue Type: Bug
> Components: MLlib
> Affects Versions: 1.4.0
> Reporter: Meihua Wu
> Priority: Critical
>
> In the BLAS wrapper, gemm is supposed to update matrix C to be alpha * A * B + beta * C. However, the current implementation will not update C as long as alpha == 0. This is incorrect when beta is not equal to 1.
> Example:
> val p = 3
> val a = DenseMatrix.zeros(p,p)
> val b = DenseMatrix.zeros(p,p)
> var c = DenseMatrix.eye(p)
> BLAS.gemm(0, a, b, 5, c)
> c is unchanged in the Spark 1.4 even though it should be multiplied by 5 element-wise.
> The bug is caused by the following in BLAS.gemm:
> if (alpha == 0.0) {
> logDebug("gemm: alpha is equal to 0. Returning C.")
> }
> Will submit PR to fix this.
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