Asymptotic optimality and minimal complexity of classification by random projection. (arXiv:2108.06339v1 [cs.LG])

The generalization error of a classifier is related to the complexity of the
set of functions among which the classifier is chosen. Roughly speaking, the
more complex the family, the greater the potential disparity between the
training error and the population error of the classifier. This principle is
embodied in layman’s terms by Occam’s razor principle, which suggests favoring
low-complexity hypotheses over complex ones. We study a family of
low-complexity classifiers consisting of thresholding the one-dimensional
feature obtained by projecting the data on a random line after embedding it
into a higher dimensional space parametrized by monomials of order up to k.
More specifically, the extended data is projected n-times and the best
classifier among those n (based on its performance on training data) is chosen.
We obtain a bound on the generalization error of these low-complexity
classifiers. The bound is less than that of any classifier with a non-trivial
VC dimension, and thus less than that of a linear classifier. We also show
that, given full knowledge of the class conditional densities, the error of the
classifiers would converge to the optimal (Bayes) error as k and n go to
infinity; if only a training dataset is given, we show that the classifiers
will perfectly classify all the training points as k and n go to infinity.



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