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From prasenjit mukherjee <>
Subject PLSI/EM in pig. Getting stuck in local minima ?
Date Mon, 09 Feb 2009 15:01:24 GMT
   I have written a pig script which attempts to implement  the EM algo for
PLSI. For extremely simple case with the following data :
transaction_log = (u1,s1), (u2,s2)
z = 2

if I initialize the p(s|z) and p(z|u)  with  equal probabilities (all 0.5 )
I was expecting a convergence of results towards ==> p(z1|u1) ~ 1  and
p(z2|u2) ~ 1.

But it seems to get stuck with the same values after the first iteration. Is
it because I am working with too less a data and getting stuck in a local
minima or there is indeed a problem with my implementation which needs to be

I also tried manually computing with those iterations and even then I am
getting same values for p(s|z) and p(z|u) with which I had started.

Any help is greatly appreciated.


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