mahout-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From prasenjit mukherjee <prasen....@gmail.com>
Subject Re: PLSI/EM in pig. Getting stuck in local minima ?
Date Tue, 10 Feb 2009 09:10:31 GMT
Thanks Pallavi for reminding :)

Yep it works when random probabilities are used.

-Prasen

On Tue, Feb 10, 2009 at 2:20 PM, Pallavi Palleti <
pallavi.palleti@corp.aol.com> wrote:

> Hi Prasen,
>  I faced the  same issue and figured out that, when you use equal
> probabilities for both P(s/z) and P(z/u), it will average out and finally
> end up with the same probability that you have started with. In order to
> make it work, one of it should be random either P(s/z) and P(z/u). Then it
> will converge.
>
> Thanks
> Pallavi
>
> prasenjit mukherjee wrote:
>
>> Hi,
>>   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
>> fixed.
>>
>> 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.
>>
>> -Thanks,
>> Prasen
>>
>>
>>
>
>

Mime
  • Unnamed multipart/alternative (inline, None, 0 bytes)
View raw message