Spreading of Sets in Product Spaces and Hypercontraction of the Markov Operator
Ahlswede, Rudolf ; Gacs, Peter
Ann. Probab., Tome 4 (1976) no. 6, p. 925-939 / Harvested from Project Euclid
For a pair of random variables, $(X, Y)$ on the space $\mathscr{X} \times \mathscr{Y}$ and a positive constant, $\lambda$, it is an important problem of information theory to look for subsets $\mathscr{A}$ of $\mathscr{X}$ and $\mathscr{B}$ of $\mathscr{Y}$ such that the conditional probability of $Y$ being in $\mathscr{B}$ supposed $X$ is in $\mathscr{A}$ is larger than $\lambda$. In many typical situations in order to satisfy this condition, $\mathscr{B}$ must be chosen much larger than $\mathscr{A}$. We shall deal with the most frequently investigated case when $X = (X_1,\cdots, X_n), Y = (Y_1,\cdots, Y_n)$ and $(X_i, Y_i)$ are independent, identically distributed pairs of random variables with a finite range. Suppose that the distribution of $(X, Y)$ is positive for all pairs of values $(x, y)$. We show that if $\mathscr{A}$ and $\mathscr{B}$ satisfy the above condition with a constant $\lambda$ and the probability of $\mathscr{B}$ goes to 0, then the probability of $\mathscr{A}$ goes even faster to 0. Generalizations and some exact estimates of the exponents of probabilities are given. Our methods reveal an interesting connection with a so-called hypercontraction phenomenon in theoretical physics.
Publié le : 1976-12-14
Classification:  Multiuser communication,  Markov operator,  Kullback $I$-divergence,  common information,  maximal correlation,  hypercontraction,  94A15,  60J35
@article{1176995937,
     author = {Ahlswede, Rudolf and Gacs, Peter},
     title = {Spreading of Sets in Product Spaces and Hypercontraction of the Markov Operator},
     journal = {Ann. Probab.},
     volume = {4},
     number = {6},
     year = {1976},
     pages = { 925-939},
     language = {en},
     url = {http://dml.mathdoc.fr/item/1176995937}
}
Ahlswede, Rudolf; Gacs, Peter. Spreading of Sets in Product Spaces and Hypercontraction of the Markov Operator. Ann. Probab., Tome 4 (1976) no. 6, pp.  925-939. http://gdmltest.u-ga.fr/item/1176995937/