Determining Stochastic Dependence for Normally Distributed Vectors Using the Chi-Squared Metric. Valiveti, R. S. & Oommen, B. J. 26(6):975–987.
Determining Stochastic Dependence for Normally Distributed Vectors Using the Chi-Squared Metric [link]Paper  doi  abstract   bibtex   
A fundamental problem in information theory and pattern recognition involves computing and estimating the probability density function associated with a set of random variables. In estimating this density function, one can either assume that the form of the density function is known, and that we are merely estimating parameters that characterize the distribution or that no information about the density function is available. This problem has been extensively studied if the random variables are independent. If the random variables are dependent and are of the discrete sort, the problem of capturing this dependence between variables has been studied in Chow and Liu (IEEE Trans. Inf. Theory14, 462–467 (May 1968)). The analogous problem for normally distributed continuous random variables has been tackled in Chow et al. (Comput. Biomed. Res.12, 589–613 (1979)). In both these instances, the determination of the best dependence tree hinges on the well-known Expected Mutual Information Measure (EMIM) Metric. Recently Valiveti and Oommen studied the suitability of the chi-squared based metric in-lieu of the EMIM metric, for the discrete variable case (Pattern Recognition25, 1389–1400 (1992)). In this paper, we generalize the latter result and study the use of the chi-squared metric for determining dependence trees for normally distributed random vectors. We show that for such vectors, the chi-squared metric yields the optimal tree and that it is identical to the one obtained using the EMIM metric. The computation of the maximum likelihood estimate of the dependence tree is also discussed.
@Article{	  valiveti_determining_1993,
  title		= {Determining Stochastic Dependence for Normally Distributed
		  Vectors Using the Chi-Squared Metric},
  volume	= {26},
  issn		= {0031-3203},
  url		= {http://www.sciencedirect.com/science/article/pii/0031320393900622},
  doi		= {https://doi.org/10.1016/0031-3203(93)90062-2},
  abstract	= {A fundamental problem in information theory and pattern
		  recognition involves computing and estimating the
		  probability density function associated with a set of
		  random variables. In estimating this density function, one
		  can either assume that the form of the density function is
		  known, and that we are merely estimating parameters that
		  characterize the distribution or that no information about
		  the density function is available. This problem has been
		  extensively studied if the random variables are
		  independent. If the random variables are dependent and are
		  of the discrete sort, the problem of capturing this
		  dependence between variables has been studied in Chow and
		  Liu ({IEEE} Trans. Inf. Theory14, 462–467 (May 1968)).
		  The analogous problem for normally distributed continuous
		  random variables has been tackled in Chow et al. (Comput.
		  Biomed. Res.12, 589–613 (1979)). In both these instances,
		  the determination of the best dependence tree hinges on the
		  well-known Expected Mutual Information Measure ({EMIM})
		  Metric. Recently Valiveti and Oommen studied the
		  suitability of the chi-squared based metric in-lieu of the
		  {EMIM} metric, for the discrete variable case (Pattern
		  Recognition25, 1389–1400 (1992)). In this paper, we
		  generalize the latter result and study the use of the
		  chi-squared metric for determining dependence trees for
		  normally distributed random vectors. We show that for such
		  vectors, the chi-squared metric yields the optimal tree and
		  that it is identical to the one obtained using the {EMIM}
		  metric. The computation of the maximum likelihood estimate
		  of the dependence tree is also discussed.},
  pages		= {975--987},
  number	= {6},
  journaltitle	= {Pattern Recognition},
  author	= {Valiveti, R. S. and Oommen, B. J.},
  date		= {1993}
}

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