404,689 research outputs found
Invariant measures for Cartesian powers of Chacon infinite transformation
We describe all boundedly finite measures which are invariant by Cartesian
powers of an infinite measure preserving version of Chacon transformation. All
such ergodic measures are products of so-called diagonal measures, which are
measures generalizing in some way the measures supported on a graph. Unlike
what happens in the finite-measure case, this class of diagonal measures is not
reduced to measures supported on a graph arising from powers of the
transformation: it also contains some weird invariant measures, whose marginals
are singular with respect to the measure invariant by the transformation. We
derive from these results that the infinite Chacon transformation has trivial
centralizer, and has no nontrivial factor. At the end of the paper, we prove a
result of independent interest, providing sufficient conditions for an infinite
measure preserving dynamical system defined on a Cartesian product to decompose
into a direct product of two dynamical systems
On the Hardness of Entropy Minimization and Related Problems
We investigate certain optimization problems for Shannon information
measures, namely, minimization of joint and conditional entropies ,
, , and maximization of mutual information , over
convex regions. When restricted to the so-called transportation polytopes (sets
of distributions with fixed marginals), very simple proofs of NP-hardness are
obtained for these problems because in that case they are all equivalent, and
their connection to the well-known \textsc{Subset sum} and \textsc{Partition}
problems is revealed. The computational intractability of the more general
problems over arbitrary polytopes is then a simple consequence. Further, a
simple class of polytopes is shown over which the above problems are not
equivalent and their complexity differs sharply, namely, minimization of
and is trivial, while minimization of and
maximization of are strongly NP-hard problems. Finally, two new
(pseudo)metrics on the space of discrete probability distributions are
introduced, based on the so-called variation of information quantity, and
NP-hardness of their computation is shown.Comment: IEEE Information Theory Workshop (ITW) 201
Ethics of Shared Decision-Making for Advanced Heart Failure Patients
This article argues that caregivers have an ethical duty to ensure that shared decision making and palliative care measures are fully discussed with and understood by their advanced heart failure patients. This is not a trivial issue. Heart failure is reaching epidemic proportions, while advances in treatment options available for heart failure patients have made it possible to prolong the life of many patients. The potential benefits and burdens of available treatments must be clearly understood by the heart failure patient so the patient can make decisions consistent with his or her values and wishes. However, too often patients are not given full information about how such treatments will affect their quality of life or about appropriate palliative care measures. The solution to this problem requires shared decision-making about treatments and palliative care measures to ensure proper goal setting, reevaluation with changes in prognosis, and end of life preparedness planning
Poisson-Furstenberg boundary and growth of groups
We study the Poisson-Furstenberg boundary of random walks on permutational
wreath products. We give a sufficient condition for a group to admit a
symmetric measure of finite first moment with non-trivial boundary, and show
that this criterion is useful to establish exponential word growth of groups.
We construct groups of exponential growth such that all finitely supported (not
necessarily symmetric, possibly degenerate) random walks on these groups have
trivial boundary. This gives a negative answer to a question of Kaimanovich and
Vershik.Comment: 24 page
Invariant measures concentrated on countable structures
Let L be a countable language. We say that a countable infinite L-structure M
admits an invariant measure when there is a probability measure on the space of
L-structures with the same underlying set as M that is invariant under
permutations of that set, and that assigns measure one to the isomorphism class
of M. We show that M admits an invariant measure if and only if it has trivial
definable closure, i.e., the pointwise stabilizer in Aut(M) of an arbitrary
finite tuple of M fixes no additional points. When M is a Fraisse limit in a
relational language, this amounts to requiring that the age of M have strong
amalgamation. Our results give rise to new instances of structures that admit
invariant measures and structures that do not.Comment: 46 pages, 2 figures. Small changes following referee suggestion
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