2. This problem explores various aspects of variance estimation in nonparametric re- gression. n-tr(S) We have the usual model y = f + where y is the n-vector of observations, f is the n-vector of unknown function values at each z₁, and e is an n-vector with mean 0 and covariance matrix Io². Suppose we estimate f nonparametrically by a linear smoother Sy. Then, by analogy with the linear model, a reasonable estimate of o² is s²-ly-Syll For the linear model S is the 'hat' matrix H which maps observations to fitted values. Here S is a smoothing matrix and depends on the smoothing parameter A, but I have suppressed this dependence for convenience. Unfortunately, while s2 is unbiased for the standard linear model, this is no longer the case for nonparametric smoothers. Verify this by showing that: Elly-Syl²)=o²n-2tr (S) + tr(STS)] + b²b. where b=f-Sf represents the smoothing bias. Note: This suggests an approximately unbiased alternative estimator, if b=0; see, for (0000)
2. This problem explores various aspects of variance estimation in nonparametric re- gression. n-tr(S) We have the usual model y = f + where y is the n-vector of observations, f is the n-vector of unknown function values at each z₁, and e is an n-vector with mean 0 and covariance matrix Io². Suppose we estimate f nonparametrically by a linear smoother Sy. Then, by analogy with the linear model, a reasonable estimate of o² is s²-ly-Syll For the linear model S is the 'hat' matrix H which maps observations to fitted values. Here S is a smoothing matrix and depends on the smoothing parameter A, but I have suppressed this dependence for convenience. Unfortunately, while s2 is unbiased for the standard linear model, this is no longer the case for nonparametric smoothers. Verify this by showing that: Elly-Syl²)=o²n-2tr (S) + tr(STS)] + b²b. where b=f-Sf represents the smoothing bias. Note: This suggests an approximately unbiased alternative estimator, if b=0; see, for (0000)
MATLAB: An Introduction with Applications
6th Edition
ISBN:9781119256830
Author:Amos Gilat
Publisher:Amos Gilat
Chapter1: Starting With Matlab
Section: Chapter Questions
Problem 1P
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