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Revision #1 to TR12-056 | 1st June 2012 03:13

Attribute-Efficient Learning and Weight-Degree Tradeoffs for Polynomial Threshold Functions

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Revision #1
Authors: Rocco Servedio, Li-Yang Tan, Justin Thaler
Accepted on: 1st June 2012 03:13
Downloads: 401
Keywords: 


Abstract:

We study the challenging problem of learning decision lists attribute-efficiently, giving both positive and negative results.

Our main positive result is a new tradeoff between the running time and mistake bound for learning length-$k$ decision lists over $n$ Boolean variables. When the allowed running time is relatively high, our new mistake bound improves significantly on the mistake bound of the best previous algorithm of Klivans and Servedio.

Our main negative result is a new lower bound on the weight of any degree-$d$ polynomial threshold function (PTF) that computes a particular decision list over $k$ variables (the ODD-MAX-BIT function). The main result of Beigel [Beigel94] is a weight lower bound of $2^{\Omega(k/d^2)}$, which was shown to be essentially optimal for $d \leq k^{1/3}$ by Klivans and Servedio. Here we prove a $2^{\Omega(\sqrt{k/d})}$ lower bound, which improves on Beigel's lower bound for $d > k^{1/3}.$ This lower bound establishes strong
limitations on the effectiveness of the Klivans and Servedio approach and suggests that it may be difficult to improve on our positive result. The main tool used in our lower bound is a new variant of Markov's classical inequality which may be of independent interest; it provides a bound on the derivative of a univariate polynomial in terms of both its degree and the size of its coefficients.


Paper:

TR12-056 | 1st May 2012 19:59

Attribute-Efficient Learning and Weight-Degree Tradeoffs for Polynomial Threshold Functions


Abstract:

We study the challenging problem of learning decision lists attribute-efficiently, giving both positive and negative results.

Our main positive result is a new tradeoff between the running time and mistake bound for learning length-$k$ decision lists over $n$ Boolean variables. When the allowed running time is relatively high, our new mistake bound improves significantly on the mistake bound of the best previous algorithm of Klivans and Servedio.

Our main negative result is a new lower bound on the weight of any degree-$d$ polynomial threshold function (PTF) that computes a particular decision list over $k$ variables (the ODD-MAX-BIT function). The main result of Beigel [Beigel94] is a weight lower bound of $2^{\Omega(k/d^2)}$, which was shown to be essentially optimal for $d \leq k^{1/3}$ by Klivans and Servedio. Here we prove a $2^{\Omega(\sqrt{k/d})}$ lower bound, which improves on Beigel's lower bound for $d > k^{1/3}.$ This lower bound establishes strong
limitations on the effectiveness of the Klivans and Servedio approach and suggests that it may be difficult to improve on our positive result. The main tool used in our lower bound is a new variant of Markov's classical inequality which may be of independent interest; it provides a bound on the derivative of a univariate polynomial in terms of both its degree and the size of its coefficients.



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