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Learning the Switching Rate by Discretising Bernoulli Sources Online
Proceedings of the Twelfth International Conference on Artificial Intelligence and Statistics, PMLR 5:432-439, 2009.
Abstract
The expert tracking algorithm Fixed-Share depends on a parameter alpha, called the switching rate. If the final number of outcomes T is known in advance, then the switching rate can be learned with regret 12logT+O(1) bits. The current fastest method that achieves this, Learn-alpha, is based on optimal discretisation of the Bernoulli distributions into O(√T) bins and runs in (T√T) time; however the exact locations of these points have to be determined algorithmically. This paper introduces a new discretisation scheme with the same regret bound for known T, that specifies the number and positions of the discretisation points explicitly. The scheme is especially useful when T is not known in advance: a new fully online algorithm, Refine-Online, is presented, which runs in O(T√TlogT) time and achieves a regret of 12log3logT+O(loglogT) bits.