Why some encoders called setProbs(2)

[冯超]

Hello everyone,
    I am a freshman in mahout, today I read the example code of the mahout
and found one line in TrainNewsGroups.java:
    NewsgroupHelper helper = new NewsgroupHelper();
    helper.getEncoder().setProbes(2);

    I referred some materials and they said it set the position of the
feature in the vector. But I've no idea why it should be set as 2 not 1 for
the word-like feature?

    Thank you very much

-- 
        Best Regards
Feng Chao