%
% spec2eq.m - this MATLAB file simulates the 
% 2-species difference equation:
%       x(n+1) = x(n) (1 - y(n))
%       y(n+1) = y(n) (x(n) -1)
% which has a line of equilibria (K,0) for any K. 
% The user is prompted to read in the value
% of x0 and y0 which must be in (0,1)
% and the time interval over which to run the 
% simulation.
!c:
s=1;
while s>0;
x0=input('input initial population x0:     ')
y0=input('input initial population x0:     ')
n=input('end of time interval b:     ')
x=zeros(n+1,1);
y=zeros(n+1,1);
t=zeros(n+1,1);
x(1)=x0;
y(1)=y0;
for i=1:n
t(i)=i-1;
x(i+1)=x(i)*(1-y(i));
y(i+1)=y(i)*(x(i)-1);
end
t(n+1)=n;
plot(t,x,t,x,'o')
title('x values'),pause
plot(t,y,t,y,'o')
title('y values'),pause
s=input('Do you want to stop - if so enter 0')
end