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From "Andrew Palumbo (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAHOUT-1531) Remove ALPHA_I CLI option in NB
Date Wed, 30 Apr 2014 13:53:14 GMT

    [ https://issues.apache.org/jira/browse/MAHOUT-1531?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13985537#comment-13985537
] 

Andrew Palumbo commented on MAHOUT-1531:
----------------------------------------

Apologies.. There is some literature that discusses optimizing a single smoothing parameter
for all words later cited by Rennie:

http://stat.rutgers.edu/home/tzhang/papers/ir01_textcat.pdf (Sec 4.1)

Although it doesn't exactly follow the weight calculation outlined in Rennie, there could
be cases where it could be useful to allow the user to set ALPHA_I.  I'll make the necessary
changes to the docs.

Please disregard this JIRA.



 

> Remove ALPHA_I CLI option in NB
> -------------------------------
>
>                 Key: MAHOUT-1531
>                 URL: https://issues.apache.org/jira/browse/MAHOUT-1531
>             Project: Mahout
>          Issue Type: Bug
>          Components: Classification, CLI
>    Affects Versions: 0.9
>         Environment:  
>            Reporter: Andrew Palumbo
>            Priority: Trivial
>             Fix For: 1.0
>
>         Attachments: MAHOUT-1531.patch
>
>
> The APLHA_I CLI option accepts a float for what should (according to the paper) be a
vector of floats (or more correctly a path to a SequenceFile containing word, alpha_i pairs
for each word in the respective dictionary).   The current MapReduce NB implementation treats
APLHA_I as a constant float where it should be a vector (ALPHA) of floats (smoothing parameter
per word).  
> However as (Rennie et al.) sec 2.2 uses a constant ALPHA_I = 1 and the NB implementation
defaults to APLHA_I = 1 and is an implementation of Rennie, there is not really a problem.
> To avoid confusion, I think its a good idea to remove the option to set ALPHA_I and to
keep ALPHA_I a constant 1.0 in NB.
>    



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