Meihua Wu created SPARK-9175:
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Summary: 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
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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