Adaptive and optimal online linear regression on l1-balls

  • Authors:
  • Sebastien Gerchinovitz;Jia Yuan Yu

  • Affiliations:
  • École Normale Supérieure, Paris, France;École Normale Supérieure, Paris, France and HEC Paris, CNRS, Jouy-en-Josas, France

  • Venue:
  • ALT'11 Proceedings of the 22nd international conference on Algorithmic learning theory
  • Year:
  • 2011

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Abstract

We consider the problem of online linear regression on individual sequences. The goal in this paper is for the forecaster to output sequential predictions which are, after T time rounds, almost as good as the ones output by the best linear predictor in a given l1-ball in Rd. We consider both the cases where the dimension d is small and large relative to the time horizon T. We first present regret bounds with optimal dependencies on the sizes U, X and Y of the l1-ball, the input data and the observations. The minimax regret is shown to exhibit a regime transition around the point d = √TUX/(2Y ). Furthermore, we present efficient algorithms that are adaptive, i.e., that do not require the knowledge of U, X, Y, and T, but still achieve nearly optimal regret bounds.