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Henry Towsner
Nonstandard convergence gives bounds on jumps
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Published: |
August 15, 2019. |
Keywords: |
ergodic theorem, metastable convergence, variation bounds. |
Subject: |
03H05, 37A25. |
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Abstract
If we know that some kind of sequence always converges, we can ask how quickly and how uniformly it converges.
Many convergent sequences converge non-uniformly and, relatedly, have no computable rate of convergence. However
proof-theoretic ideas often guarantee the existence of a uniform ``meta-stable'' rate of convergence.
We show that obtaining a stronger bound---a uniform bound on the number of jumps the sequence makes---is equivalent to being able to strengthen convergence to occur in the nonstandard numbers. We use this to obtain bounds on the number of jumps in nonconventional ergodic averages. |
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Acknowledgements
Partially supported by NSF grant DMS-1600263.
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Author information
Henry Towsner:
Department of Mathematics
University of Pennsylvania
209 South 33rd Street
Philadelphia, PA 19104-6395, USA
htowsner@math.upenn.edu
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