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
