Github user jkbradley commented on the pull request:

    https://github.com/apache/spark/pull/1269#issuecomment-67083325
  
    @akopich   Thanks for the updates!  (Much easier to see the diff now)
    
    The decision about setters vs. constructor arguments was from [this JIRA 
(design doc linked from 
JIRA)](https://issues.apache.org/jira/browse/SPARK-3530).  The main issues were 
binary compatibility (adding a new parameter to an algorithm requires adding a 
new constructor when we don't use setters) and problems with Java not 
supporting named parameters and default arguments.
    
    For testing, I agree it's tough to test "accuracy" for topic models.  It 
would be great to see comparisons on the same dataset, just to get a sense of 
whether perplexity decreases similarly and is in the same ballpark.  Same with 
scalability & speed.
    As far as other implementations, your other non-Spark implementation would 
be helpful if it's been tested before.  It would be great to see comparisons 
with other Spark LDA implementations.  E.g., 
[https://github.com/apache/spark/pull/2388] is LDA using GraphX, and it would 
be very helpful to see how performance varies.  (It might also take a bit more 
work though.)
    What sounds reasonable to you?
    
    I'm recommending this testing as separate from unit tests.  (A unit test 
for perplexity sounds a bit unstable.)  Perhaps the test code could become an 
example instead of a unit test.



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