Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A stochastic model for the evolution of the influenza virus   Consider a birth and death chain to model the number of types of a given
virus. Each type gives birth to a new type at rate $\lambda$ and dies at rate
1. Each type is also assigned a fitness. When a death occurs either the least
fit type dies (with probability $1-r$) or we kill a type at random (with
probability $r$). We show that this random killing has a large effect (for any
$r>0$) on the behavior of the model when $\lambda<1$. The behavior of the model
with $r>0$ and $\lambda<1$ is consistent with features of the phylogenetic tree
of influenza.

37
The categories of this paper are: supr-con
7
The categories of this paper are: hep-th
8
The categories of this paper are: hep-ex
25
The categories of this paper are: patt-sol
19
The categories of this paper are: eess
28
The categories of this paper are: alg-geom
29
The categories of this paper are: funct-an
20
The categories of this paper are: acc-phys
23
The categories of this paper are: solv-int
18
The categories of this paper are: econ
22
The categories of this paper are: chao-dyn
21
The categories of this paper are: adap-org
17
The categories of this paper are: q-fin
4
The categories of this paper are: cond-mat
36
The categories of this paper are: cmp-lg
31
The categories of this paper are: ao-sci