LearnNSE sbkt close to zero

[paulorla]

Dear @ALL,

In the implementation of the LearnNSE available in the MOA 2017.06, there is a chance for the sbkt variable to get really close to zero, leading to the computation of the log of infinity when calculating the ensemble weights.

this.ensembleWeights.add(Math.log(1.0 / sbkt));

This leaded to problems in the Gaussian problem suggested by the original author of the Learn++.NSE: http://users.rowan.edu/~polikar/research/NSE/

As a workaround, one of the original authors of the NSE check if the "sbkt" is smaller than 0.01. If so, the value is set to 0.01.
It can be seen in: https://github.com/gditzler/IncrementalLearning/blob/master/src/learn_nse.m

Check the condition:

if net.beta(net.t,net.t)<net.threshold,
net.beta(net.t,net.t) = net.threshold;
end

It seems to solve the problem when implemented in the MOA version of the LearnNSE.

Best regars.

[abifet]

Thanks! Can you propose a pull request with this fix?