[R] coupled ODE population model

[Justin Frank]

I'm fairly new to R, and I'm trying to write out a population model that
satisfies the following;

the system consists of s species, i= 1, 2,...,s
network of interactions between species is specified by a (s x s) real matrix,
C[i,j]

x[i] being the relative population of the "ith" species (0 =< x[i] =< 1,
sum(x[i]=1)

the evolution rule being considered is as follows;

xprime[i] = f[i] if x[i] > 0 or f[i] >= 0

xprime[i] = 0 if x[i] = 0 and f[i] < 0

where f[i] = sum(C[i,j]*x[j]) - x[i]*sum(C[k,j]*x[j])


I have a bit of attempted code written out, but are there any tricks or tips
that would condense or make this mess look nicer?

-Justin