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arXiv 1302.2677math.STstat.TH
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用图模型估计大精度矩阵的后验收敛速度

Posterior convergence rates for estimating large precision matrices using graphical models

Sayantan Banerjee, Subhashis Ghosal

摘要:

当$p$可能远大于可用样本量$n$时,我们考虑$p\times p$精度矩阵的贝叶斯估计。众所周知,在这种超高维情况下的一致估计需要正则化,例如条带化、锥形化或阈值化。我们在模型中考虑带状结构,并通过高斯图模型在带状精度矩阵上引入先验分布,其中只有当两个顶点在给定距离内时才存在边。在适当选择图的阶数的情况下,得到了在一类精度矩阵上基于图模型的后验分布和Bayes估计在$L_{\infty}$ -算子范数下的一致收敛速度,即使真精度矩阵可能不具有带状结构.在证明的过程中,我们还计算了极大似然估计(MLE)在相同条件下的收敛速度,这是独立的兴趣。基于图模型的极大似然估计和贝叶斯估计是自动正定的,这是文献中其他估计所不具备的一个理想性质。我们还进行了模拟研究,以比较有限样本的贝叶斯估计和极大似然估计的性能的基础上的图形模型,通过使用Cholesky分解的精度矩阵。最后讨论了利用边缘似然函数选择图模型阶数的实用方法。

英文摘要:

We consider Bayesian estimation of a $p\times p$ precision matrix, when $p$ can be much larger than the available sample size $n$. It is well known that consistent estimation in such ultra-high dimensional situations requires regularization such as banding, tapering or thresholding. We consider a banding structure in the model and induce a prior distribution on a banded precision matrix through a Gaussian graphical model, where an edge is present only when two vertices are within a given distance. For a proper choice of the order of graph, we obtain the convergence rate of the posterior distribution and Bayes estimators based on the graphical model in the $L_{\infty}$-operator norm uniformly over a class of precision matrices, even if the true precision matrix may not have a banded structure. Along the way to the proof, we also compute the convergence rate of the maximum likelihood estimator (MLE) under the same set of condition, which is of independent interest. The graphical model based MLE and Bayes estimators are automatically positive definite, which is a desirable property not possessed by some other estimators in the literature. We also conduct a simulation study to compare finite sample performance of the Bayes estimators and the MLE based on the graphical model with that obtained by using a Cholesky decomposition of the precision matrix. Finally, we discuss a practical method of choosing the order of the graphical model using the marginal likelihood function.

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