Joseph K. Bradley created SPARK-6683:
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             Summary: GLMs with GradientDescent could scale step size instead 
of features
                 Key: SPARK-6683
                 URL: https://issues.apache.org/jira/browse/SPARK-6683
             Project: Spark
          Issue Type: Improvement
          Components: MLlib
    Affects Versions: 1.3.0
            Reporter: Joseph K. Bradley
            Priority: Minor


GeneralizedLinearAlgorithm can scale features.  This improves optimization 
behavior (and also affects the optimal solution, as is being discussed and 
hopefully fixed by [https://github.com/apache/spark/pull/5055]).

This is a bit inefficient since it requires making a rescaled copy of the data.

GradientDescent could instead scale the step size separately for each feature 
(and adjust regularization as needed; see the PR linked above).  This would 
require storing a vector of length numFeatures, rather than making a full copy 
of the data.

I haven't thought this through for LBFGS, so I'm not sure if it's generally 
usable or would require a specialization for GLMs with GradientDescent.



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