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基于边际正则藤copulas对具有既定皮尔逊相关系数的多元离散随机变量的抽样算法

Sampling multivariate count variables with prespecified Pearson correlation using marginal regular vine copulas

  • 摘要: 基于多元离散随机变量的抽样问题在实践中的应用价值,Erhardt和Czado 提出了基于C藤Copulas的多元离散随机变量的抽样算法,其优化参数为C藤的边参数,目标函数为给定的皮尔逊偏相关系数与样本偏相关系数的距离. 本文引入了边际正则藤Copulas的概念,进而直接以随机变量对的样本相关系数与给定的皮尔逊相关系数σij之间的距离为目标函数进行优化. 三组模拟实验结果分别与文献1提出的基于C藤的抽样算法,文献3中使用的Naive基准抽样算法相比,基于边际正则藤Copula的抽样算法具有相对较高的精确性.本文中所使用的抽样算法通过Python语言实现并打包命名为countvar上传至PyPi.

     

    Abstract: The problem of sampling multivariate count variables has practical significance. Ref.1proposed an algorithm for sampling multivariate count random variables based on C-vine copulas, by which the parameters
    ρi,j|D
    of edge
    ei,j|D
    of the C-vine structure are estimated by optimizing the difference between the sample partial correlation
    σ︿i,j|D
    and the partial correlation
    σi,j|D
    calculated from the prespecified correlation matrix by the Pearson recurrence formula, where
    D
    is a conditioning node set. We introduce the concept of marginal regular vine copula, which leads to directly optimizing the difference between the sample correlation
    σ︿ij
    and the targeted correlation
    σij
    for pairs of variables. Three simulation studies illustrate that the new sampling method generates more accurate results than the C-vine sampling method in Ref.1and the Naive sampling method in Ref.3. The sampling algorithm routines are implemented in Python as package countvar in PyPi.

     

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