A branching process is a stochastic process that models a population in which individuals reproduce
independently according to a common probability law. In the Galton-Watson
process, if 
is the population in generation 
and 
is the number of offspring of individual 
, then
 |
Writing 
for the expected value of the offspring count,
the process is called subcritical, critical, or supercritical according as 
, 
, or 
. Branching processes also occur in continuous time, with
spatial motion, and with more general state spaces.
