Help:=proc(a,n): print(`Hill(a,n), Extr(Prod)`):end:

#Hill(a,n): inputs a symbol a and a pos.
#integer n, outputs the solution x[i]
#of steady-state, size of population
#in i-City if the rate of flow from
#i-City to j-City is a[i,j]
Hill:=proc(a,n) local x,i,j,var,eq:

var:=[seq(x[i],i=1..n)]:


eq:=
{seq(
x[i]*add(a[i,j],j=1..n)-
add(a[j,i]*x[j],j=1..n), i=1..n)}:

var:=subs(solve(eq,{op(var)}),var):

var:=subs({seq(x[i]=1,i=1..n)},var):

for i from 1 to n do
 if var[i]<>1 then
   return [seq(var[j]*denom(var[i]),j=1..n)]:
 fi:
od:

end:





Extr:=proc(Prod) local i:

 {seq([op(op(i,Prod))],i=1..nops(Prod))}:
end:


Graphs:=proc(n,i) local a,S,j:
S:=Hill(a,n)[i]:
  {seq(Extr(op(j,S)), j=1..nops(S))}:
end: