Abstract
A beautiful result of Sarmanov (Dokl. Akad. Nauk SSSR 121(1), 52–55, 1958) says that for a Gaussian vector (X,Y), \(\operatorname {Var}(\mathbb {E}[f(Y)|X])\le \rho^{2}\operatorname {Var}(f(Y))\) for all measurable functions f, where ρ is the (linear) correlation coefficient between X and Y. We generalize this result to a general Φ-entropy (a nonlinear version of his result) by means of a previous result of D. Chafai based on Bakry–Emery’s Γ 2-technique and tensorization.
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Supported by the ANR Project “Inégalités fonctionelles” and the NSF of China.
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Wu, L. A Φ-Entropy Contraction Inequality for Gaussian Vectors. J Theor Probab 22, 983–991 (2009). https://doi.org/10.1007/s10959-009-0211-0
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DOI: https://doi.org/10.1007/s10959-009-0211-0