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https://issues.apache.org/jira/browse/MAHOUT-399?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12871039#action_12871039
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Michael Lazarus commented on MAHOUT-399:
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Hi David,
Thank you for responding. I agree that you can arrive at different results
with slightly different implementations. And also sometimes LDA gets stuck in
a local minimum. In the pdf, for example, looking at the log-likelihood of the
corpus given the model across models with different numbers of topics, you can
see that Blei's implementation of LDA gets stuck on a ten topic model.
This dataset was designed to have just enough structure to demonstrate some of
the behavior of the algorithm while at the same time defining an underlying
model that should be readily discoverable by an implementation.
I have found it useful in debugging various systems that use LDA.
Thanks,
Mike.
> LDA on Mahout 0.3 does not converge to correct solution for overlapping
> pyramids toy problem.
> ---------------------------------------------------------------------------------------------
>
> Key: MAHOUT-399
> URL: https://issues.apache.org/jira/browse/MAHOUT-399
> Project: Mahout
> Issue Type: Bug
> Components: Classification
> Affects Versions: 0.3
> Environment: Mac OS X 10.6.2, Hadoop 0.20.2, Mahout 0.3.
> Reporter: Michael Lazarus
> Priority: Critical
> Attachments: olt.tar, Overlapping Pyramids Toy Dataset.pdf
>
>
> Hello,
> Apologies if I have not labeled this correctly.
> I have run a toy problem on Mahout 0.3 (locally) for LDA that I used to test
> Blei's c version of LDA that he posts on his site. It has an exact solution
> that the LDA should converge to. Please see attached PDF that describes the
> intended output.
> Is LDA working? The following output indicates some sort of collapsing
> behavior to me.
> T0 T1 T2 T3 T4
> x w x u x
> u u g j n
> l r i m l
> j q h h p
> v p e i q
> e t f g v
> d s d f o
> b c b n k
> y f c l m
> w v u v u
> c d p y t
> k o l r r
> i b j k j
> f e k e f
> g x y s y
> t y w b w
> h i s p s
> o l v x d
> q j t d i
> n k o t b
> The intended output is (again, please see attached):
> D I N S X
> d i n s x
> c h m t y
> e j o r w
> b k l u v
> f g p q a
> a f k p b
> g l q v u
> h m j w t
> y u r o c
> n s d d i
> s e x f f
> r q i i n
> m v w c o
> o w u a h
> q n s h g
> p t c x d
> t x f e l
> x d e j s
> w y g b j
> i r y n r
> u o h y m
> k b t l e
> v c a m k
> j a b g p
> l p v k q
> What tests do you run to make sure the output is correct?
> Thank you,
> Mike.
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