%eks 10.21
n=120;
h=.1;
y=zeros(n+1,1);
z=zeros(n+1,1);
y(1)=1.5;
z(1)=1.5;

for i = 1:n
    y(i+1)=y(i)+h*y(i)*(2-z(i));
    z(i+1)=z(i)+h*z(i)*(y(i)-1);
end

plot(y,z)