熵损失下协方差矩阵最佳仿射同变估计的改进
Improvement on the Best Affine Equivariant Estimation of the Covariance Matrix under the Entropy Loss
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摘要: 设X1,…, Xn (n>p)是来自多元正态分布Np(μ, ∑)的一个样本,其中μ ∈RP ,∑>0均未知.本文在熵损失 L(\widehat\Sigma, \Sigma)=\operatornametr\left(\Sigma^-1 \widehat\Sigma\right)-\log \left|\Sigma^-1 \widehat\Sigma\right|-p下证明了协方差矩阵∑的最佳仿射同变估计是不容许的,且给出了其改进估计。Abstract: Let X1,…, Xn (n>p) be a random sample from multivariate normal distribution Np(μ, ∑), where μ ∈RP and ∑ is a positive definite matrix, both μ and ∑ being unknown. In this paper it is shown for the entropy loss L(\widehat\Sigma, \Sigma)=\operatornametr\left(\Sigma^-1 \widehat\Sigma\right)-\log \left|\Sigma^-1 \widehat\Sigma\right|-p the best affine equivariant estimator of the covariance matrix ∑ is inadmissible and an improved estimator is explicitly constructed.