
Recent Posts
 An arithmetic van der Corput trick and the polynomial van der Waerden theorem
 Piecewise syndetic sets, topological dynamics and ultrafilters
 Measure preserving actions of affine semigroups and {x+y,xy} patterns
 Szemerédi Theorem Part VI – Dichotomy between weak mixing and compact extension
 Gaussian systems
Category Archives: Analysis
The horocycle flow is mixing of all orders
— 1. Introduction — The main purpose of this post is to present a proof, due to Brian Marcus, that the horocycle flow is mixing of all orders. The precise definition of mixing of all orders for actions is given … Continue reading
Posted in Analysis, Classic results, Ergodic Theory
Tagged flows, horocycle flow, Marcus, mixing of all orders, van der Corput
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Large subsets of discrete hypersurfaces in Z^d contain arbitrarily many collinear points
— 1. Introduction — Recently, Florian Richter and I uploaded to the arXiv our paper titled `Large subsets of discrete hypersurfaces in contain arbitrarily many collinear points’. This was the outcome of a fun project which started when we learned … Continue reading
Posted in Analysis, Combinatorics, paper
Tagged Banach density, collinear points, Lipschitz, Pomerance, Rademacher's theorem, Richter
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Convergence of continuous function
A few years back I was playing with the strong law of large numbers (essentially I wanted to understand pointwise convergence for averages over sets other than ) following Etemadi’s proof. This didn’t lead anywhere in the end (essentially because … Continue reading
Ergodic Decomposition
— 1. Introduction — In the study of measurable dynamics, the basic object of study is a measure preserving system: a quadruple , where is a set, is a algebra over , is a probability measure on and is a … Continue reading
Posted in Analysis, Classic results, Ergodic Theory, Tool
Tagged Choquet theorem, disintegration of measures, ergodic decomposition
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Disintegration of measures
In this post I will talk about conditional expectation and disintegration of a measure with respect to a algebra. All this is classical probability theory but I think not many people (me included) come across this in a standard course … Continue reading
Posted in Analysis, Classic results, Tool
Tagged conditional expectation, disintegration of measure, measure theory
6 Comments
Weak Mixing
— 1. Introduction — When studying measure preserving systems (defined below) there are many important classes that are worth studying separately. One way to distinguish between different classes is the level of “mixing” or “randomness” of the system. In this … Continue reading
Posted in Analysis, Ergodic Theory
Tagged idempotents, minimal, Ultrafilters, van der Corput, weak mixing
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The Ergodic Theorem
— 1. Introduction — One can argue that (modern) ergodic theory started with the ergodic Theorem in the early 30’s. Vaguely speaking the ergodic theorem asserts that in an ergodic dynamical system (essentially a system where “everything” moves around) the … Continue reading
Posted in Analysis, Classic results, Ergodic Theory, Tool
Tagged Akcoglu, Birkhoff, del Junco, ergodic theorem, Lindenstrauss, Rohlin, Rokhlin, von Neumann
4 Comments