%
%  code12Wb.m -- 20 nov 02 -- djm
%
%  - single population code

clear
global ODE r1 a1 r2 a2 s1 s2

%  set ODE choice

disp(' ')
disp(' ODE choices:')
disp('   1) two limited populations')
disp('   2) grass & cattle')
disp('   3) grass & hungry cattle')
disp('   4) example 2, page 495')
disp(' ')
setup = input('choose 1/2/3/4/R:  ');
disp(' ')
disp(' click to choose IV (bottom to quit)')
disp(' ')

switch setup
    case{1}
        ODE = 1;
        r1 =  1;  a1 = 0.5;  r2 =  1;  a2 = 0.5;
        s1 = 0;  s2 = 0;
    case{2}
        ODE = 1;
        r1 =  1;  a1 = 0.5;  r2 =  1;  a2 = 0.5;
        s1 = 0.2;  s2 = 0;
    case{3}
        ODE = 1;
        r1 =  1;  a1 = 0.5;  r2 =  1;  a2 = 0.5;
        s1 = 1.2;  s2 = 0;
    case{4}
        ODE = 2;
        r1 =  1;  a1 = 1;  r2 =  0.5;  a2 = 0.25;
        s1 = 1;  s2 = 0.75;
    otherwise
        break
end
   
figure(1);  clf;  hold on
title('\bf population phase plane')
xlabel('\bf y(t)-axis')
ylabel('\bf z(t)-axis')
axis([0 4 0 4])

IV = [];

while (isempty(IV))
    click = ginput(1);
    IV = click;
   
    if(IV(2)<0)
        break
    end
    
%  invoke runge-kutta solver
    
    opt = odeset('RelTol',1e-3,'AbsTol',1e-6);
    [t y] = ode45(@Fode12Wb,[0 10],IV,opt);

    plot(y(:,1),y(:,2),'r')
    plot(IV(1),IV(2),'ko')
    
    IV = [];
end