Clear Filters
Clear Filters

Fixing code to plot an ODE

1 view (last 30 days)
frozentangled
frozentangled on 24 Dec 2020
Commented: Mischa Kim on 26 Dec 2020
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

Accepted Answer

Mischa Kim
Mischa Kim on 24 Dec 2020
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
  2 Comments
frozentangled
frozentangled on 24 Dec 2020
It worked. Thanks! I am most grateful
I hope you have a great holiday season!
Mischa Kim
Mischa Kim on 26 Dec 2020
Have a joyful holiday season, as well.

Sign in to comment.

More Answers (0)

Categories

Find more on Mathematics in Help Center and File Exchange

Tags

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!