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arXiv 1502.00665math.STstat.TH
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稀疏类上线性和二次泛函的Minimax估计

Minimax estimation of linear and quadratic functionals on sparsity classes

Olivier Collier, Laëtitia Comminges, Alexandre B. Tsybakov

摘要:

对于高斯序列模型,我们获得了非渐近极小极大估计率的线性,二次和L2-范数泛函类的稀疏向量和构造最佳估计,达到这些速度。感兴趣的主要对象是类s-稀疏向量,我们还提供完全自适应估计(独立的s和噪声方差),只有grammically慢速率比极大极小的。此外,我们还得到了Lq-球上的Minimax速率,其中0 < q < 2。这种分析表明,在一般情况下,有三个区域的收敛速度,我们称之为稀疏区,密集区和退化区,而第四个区域出现的二次函数的估计。我们证明,与向量的估计相反,稀疏区的最佳速率中的正确对数项为log(d/s^2)而不是log(d/s)。对于稀疏类,线性泛函和L2-范数的估计率在s = sqrt(d)(稀疏区和密集区之间的边界)处具有简单的弯头,并且表现出类似的性能,而二次泛函的估计揭示了更复杂的效果,并且仅基于由向量上的稀疏性条件描述的稀疏性是不可能的。最后,我们将我们的结果估计的L2-范数的问题测试稀疏的替代品。特别是,我们得到了一个非渐近模拟的Ingster-Donoho-Jin理论揭示了一些影响,没有捕捉到以前的渐近分析。

英文摘要:

For the Gaussian sequence model, we obtain non-asymptotic minimax rates of estimation of the linear, quadratic and the L2-norm functionals on classes of sparse vectors and construct optimal estimators that attain these rates. The main object of interest is the class s-sparse vectors for which we also provide completely adaptive estimators (independent of s and of the noise variance) having only logarithmically slower rates than the minimax ones. Furthermore, we obtain the minimax rates on the Lq-balls where 0 < q < 2. This analysis shows that there are, in general, three zones in the rates of convergence that we call the sparse zone, the dense zone and the degenerate zone, while a fourth zone appears for estimation of the quadratic functional. We show that, as opposed to estimation of the vector, the correct logarithmic terms in the optimal rates for the sparse zone scale as log(d/s^2) and not as log(d/s). For the sparse class, the rates of estimation of the linear functional and of the L2-norm have a simple elbow at s = sqrt(d) (boundary between the sparse and the dense zones) and exhibit similar performances, whereas the estimation of the quadratic functional reveals more complex effects and is not possible only on the basis of sparsity described by the sparsity condition on the vector. Finally, we apply our results on estimation of the L2-norm to the problem of testing against sparse alternatives. In particular, we obtain a non-asymptotic analog of the Ingster-Donoho-Jin theory revealing some effects that were not captured by the previous asymptotic analysis.

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