# Bob Pego : Merging-splitting group dynamics via Bernstein function theory (or: How to count fish using mathematics)

We study coagulation-fragmentation equations inspired by a simple model derived in fisheries science to explain data on the size distribution of schools of pelagic fish. The equations lack detailed balance and admit no H-theorem, but we are anyway able to develop a rather complete description of equilibrium profiles and large-time behavior, based on complex function theory for Bernstein and Pick (Herglotz) functions. The generating function for discrete equilibrium profiles also generates the Fuss-Catalan numbers that count all ternary trees with $n$ nodes. The structure of equilibrium profiles and other related sequences is explained through a new and elegant characterization of the generating functions of completely monotone sequences, as those Pick functions analytic and nonnegative on a half line. This is joint work with Jian-Guo Liu and Pierre Degond.

**Category**: Applied Math and Analysis**Duration**: 01:24:41**Date**: October 18, 2017 at 11:55 AM**Views**: 101-
**Tags:**seminar, Applied Math And Analysis Seminar

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