Fixing code to plot an ODE

Hi guys,

I was just coding to plot an ODE, but ran into some problems dispalying the result

The code are as follows

function dxdt = ODE(t, x, alpha, beta)
dxdt = diag(alpha - beta*[x(1);x(2);x(3)])*[x(1);x(2);x(3)];

for n=1:200
p=.01*n;
alpha=[.1; .5; .3];
beta=[.2 .3 .4; p 1.5 .6; .2 .5 .8];
time = [0 100];
initial=[0.5; 0.2; 0.3];
[t,y] = ode45(@(t,y) ODE(t,y,alpha,beta), time, initial);
F1=y(100,1);
F2=y(100,2);
F3=y(100,3);
end

figure(1)
plot(p,F1);
hold on
plot(p,F2);
plot(p,F3);
hold off

Could you tell me what's off?

Many thanks in advance

Answer 1

[Mischa Kim]

Hi, you are almost there. This should get you started:

hold on
for n=1:200
    p=.01*n;
    alpha=[.1; .5; .3];
    beta=[.2 .3 .4; p 1.5 .6; .2 .5 .8];
    time = [0 100];
    initial=[0.5; 0.2; 0.3];
    [t,y] = ode45(@(t,y) ODE(t,y,alpha,beta), time, initial);
    F1=y(end,1); % assuming you are trying to access last elements
    F2=y(end,2);
    F3=y(end,3);
    
    plot(p,F1,'ro'); % a cleaner way would be to save the values... 
    hold on          % ...for Fi in a matrix and then plot outside...
    plot(p,F2,'ko'); % ...of the for loop
    plot(p,F3,'bo');
end
hold off

function dxdt = ODE(t, x, alpha, beta)
dxdt = diag(alpha - beta*[x(1);x(2);x(3)])*[x(1);x(2);x(3)];
end

[frozentangled]

It worked. Thanks! I am most grateful

I hope you have a great holiday season!

[Mischa Kim]

Have a joyful holiday season, as well.